<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019eb325-40e9-7472-a7ac-f49dd677bd3c,g:6f053bfb-6a7b-42a9-aaf0-d4b3e1d9b2f4-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="https://xbrl.org/2023/arcrole/summation-item" xlink:type="simple" xlink:href="https://www.xbrl.org/2023/calculation-1.1.xsd#summation-item"/>
  <link:roleRef roleURI="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="isba-20260630.xsd#INTERIMCONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019eb325-4869-7e25-a6c6-c83c2e2e6b34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-4869-7f53-8f9c-8a261bd1e294" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019eb325-4869-7e25-a6c6-c83c2e2e6b34" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-4869-7f53-8f9c-8a261bd1e294" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019eb325-4869-7d47-aae0-a055e1a3bc81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019eb325-4869-7e25-a6c6-c83c2e2e6b34" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019eb325-4869-7d47-aae0-a055e1a3bc81" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eb325-4869-7cf2-a958-df08bfbcb789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019eb325-4869-7fb3-b258-bf0859e26353" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_019eb325-4869-7cf2-a958-df08bfbcb789" xlink:to="loc_us-gaap_CommonStockValue_019eb325-4869-7fb3-b258-bf0859e26353" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_DeferredCompensationArrangementwithIndividualDeferredCompensationObligations_019eb325-4869-7499-a87c-94b8b288111f" xlink:href="isba-20260630.xsd#isba_DeferredCompensationArrangementwithIndividualDeferredCompensationObligations"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_019eb325-4869-7cf2-a958-df08bfbcb789" xlink:to="loc_isba_DeferredCompensationArrangementwithIndividualDeferredCompensationObligations_019eb325-4869-7499-a87c-94b8b288111f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019eb325-4869-7f1a-849e-8c7fe98a086c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_019eb325-4869-7cf2-a958-df08bfbcb789" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019eb325-4869-7f1a-849e-8c7fe98a086c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019eb325-4869-7e97-b100-9b7c395732b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_019eb325-4869-7cf2-a958-df08bfbcb789" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019eb325-4869-7e97-b100-9b7c395732b5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019eb325-4869-75cf-a633-3e898bfa60fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019eb325-4869-720d-9f76-904ddf2cb3bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_019eb325-4869-75cf-a633-3e898bfa60fe" xlink:to="loc_us-gaap_Liabilities_019eb325-4869-720d-9f76-904ddf2cb3bf" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019eb325-4869-700c-a4af-31c6c0e50f8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_019eb325-4869-75cf-a633-3e898bfa60fe" xlink:to="loc_us-gaap_StockholdersEquity_019eb325-4869-700c-a4af-31c6c0e50f8a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019eb325-4869-779f-b7ee-bc54fb9f19af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019eb325-4869-779f-b7ee-bc54fb9f19af" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-7c36-8723-3a161a74cc60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-7c36-8723-3a161a74cc60" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableHeldForSaleAmount_019eb325-4869-7de6-b3a6-9ff8b338319e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansReceivableHeldForSaleAmount"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_LoansReceivableHeldForSaleAmount_019eb325-4869-7de6-b3a6-9ff8b338319e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019eb325-4869-7188-9d61-36699d2a7363" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss_019eb325-4869-7188-9d61-36699d2a7363" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStock_019eb325-4869-7f93-92b5-dee8ec4ca607" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankStock"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_FederalHomeLoanBankStock_019eb325-4869-7f93-92b5-dee8ec4ca607" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019eb325-4869-7cb1-8050-0ff78866d81b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019eb325-4869-7cb1-8050-0ff78866d81b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BankOwnedLifeInsurance_019eb325-4869-7321-8ffc-a33ea4dc139c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BankOwnedLifeInsurance"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_BankOwnedLifeInsurance_019eb325-4869-7321-8ffc-a33ea4dc139c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetIncludingGoodwill_019eb325-4869-77f0-9997-18360c4e0565" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetIncludingGoodwill"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_IntangibleAssetsNetIncludingGoodwill_019eb325-4869-77f0-9997-18360c4e0565" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivableAndOtherAssets_019eb325-4869-742d-acc7-43fa4cde2ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivableAndOtherAssets"/>
    <link:calculationArc order="9" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_019eb325-4869-71fa-99e9-45eb92797114" xlink:to="loc_us-gaap_InterestReceivableAndOtherAssets_019eb325-4869-742d-acc7-43fa4cde2ac0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Deposits_019eb325-4869-72ef-b3ba-98a5e5c3522b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Deposits"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestBearingDepositLiabilities_019eb325-4869-703c-9cac-67e1033d5f4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestBearingDepositLiabilities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Deposits_019eb325-4869-72ef-b3ba-98a5e5c3522b" xlink:to="loc_us-gaap_NoninterestBearingDepositLiabilities_019eb325-4869-703c-9cac-67e1033d5f4e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestBearingDomesticDepositDemand_019fd93f-897a-73dd-9568-30948add640e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestBearingDomesticDepositDemand"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Deposits_019eb325-4869-72ef-b3ba-98a5e5c3522b" xlink:to="loc_us-gaap_InterestBearingDomesticDepositDemand_019fd93f-897a-73dd-9568-30948add640e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsMoneyMarketDeposits_019fd93f-ccdc-7cee-acd7-edca89d8818b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsMoneyMarketDeposits"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Deposits_019eb325-4869-72ef-b3ba-98a5e5c3522b" xlink:to="loc_us-gaap_DepositsMoneyMarketDeposits_019fd93f-ccdc-7cee-acd7-edca89d8818b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositsSavingsDeposits_019fd940-13ea-74f9-a75a-e9d35f681fe6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositsSavingsDeposits"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Deposits_019eb325-4869-72ef-b3ba-98a5e5c3522b" xlink:to="loc_us-gaap_DepositsSavingsDeposits_019fd940-13ea-74f9-a75a-e9d35f681fe6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDeposits_019fd940-572d-7ee0-8425-bb46b6eb2e9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TimeDeposits"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Deposits_019eb325-4869-72ef-b3ba-98a5e5c3522b" xlink:to="loc_us-gaap_TimeDeposits_019fd940-572d-7ee0-8425-bb46b6eb2e9f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019eb325-4869-743b-9810-88400f03d87e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Deposits_019eb325-4869-7ff1-bfc2-8110c79af267" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Deposits"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_019eb325-4869-743b-9810-88400f03d87e" xlink:to="loc_us-gaap_Deposits_019eb325-4869-7ff1-bfc2-8110c79af267" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase_019eb325-4869-72e8-95ff-986fea6557c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_019eb325-4869-743b-9810-88400f03d87e" xlink:to="loc_us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase_019eb325-4869-72e8-95ff-986fea6557c8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019eb325-4869-7694-8149-de4778ec0699" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdvancesFromFederalHomeLoanBanks"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_019eb325-4869-743b-9810-88400f03d87e" xlink:to="loc_us-gaap_AdvancesFromFederalHomeLoanBanks_019eb325-4869-7694-8149-de4778ec0699" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebt_019eb325-4869-7b24-b59a-afc1b23132c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubordinatedDebt"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_019eb325-4869-743b-9810-88400f03d87e" xlink:to="loc_us-gaap_SubordinatedDebt_019eb325-4869-7b24-b59a-afc1b23132c9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019eb325-4869-7d99-a76b-6b5221dad0d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_019eb325-4869-743b-9810-88400f03d87e" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_019eb325-4869-7d99-a76b-6b5221dad0d5" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFINCOMEUNAUDITED" xlink:type="simple" xlink:href="isba-20260630.xsd#INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFINCOMEUNAUDITED"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFINCOMEUNAUDITED" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eb325-4869-7ab3-b98e-0c3d9bd65877" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019eb325-4869-772d-ba86-3fca40e8ab96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_019eb325-4869-7ab3-b98e-0c3d9bd65877" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019eb325-4869-772d-ba86-3fca40e8ab96" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations_019eb325-4869-705e-ac86-a3959021913f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_019eb325-4869-7ab3-b98e-0c3d9bd65877" xlink:to="loc_us-gaap_FederalIncomeTaxExpenseBenefitContinuingOperations_019eb325-4869-705e-ac86-a3959021913f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-7e3f-9c86-de1c98ce1acd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDividendIncomeOperating"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndFeeIncomeLoansAndLeases_019eb325-4869-70b1-ab33-05ed12e4383d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndFeeIncomeLoansAndLeases"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-7e3f-9c86-de1c98ce1acd" xlink:to="loc_us-gaap_InterestAndFeeIncomeLoansAndLeases_019eb325-4869-70b1-ab33-05ed12e4383d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeSecuritiesTaxable_019eb325-4869-79a5-86c4-d782e99b5390" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeSecuritiesTaxable"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-7e3f-9c86-de1c98ce1acd" xlink:to="loc_us-gaap_InterestIncomeSecuritiesTaxable_019eb325-4869-79a5-86c4-d782e99b5390" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeSecuritiesTaxExempt_019eb325-4869-7a2b-9f43-1c9579448e69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeSecuritiesTaxExempt"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-7e3f-9c86-de1c98ce1acd" xlink:to="loc_us-gaap_InterestIncomeSecuritiesTaxExempt_019eb325-4869-7a2b-9f43-1c9579448e69" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendIncomeOperating_019eb325-4869-7d87-84f7-c786985881c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendIncomeOperating"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-7e3f-9c86-de1c98ce1acd" xlink:to="loc_us-gaap_DividendIncomeOperating_019eb325-4869-7d87-84f7-c786985881c4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_InterestIncomeFederalFundsSoldAndOther_019eb325-4869-7f4b-9847-993c7ac2ebbc" xlink:href="isba-20260630.xsd#isba_InterestIncomeFederalFundsSoldAndOther"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-7e3f-9c86-de1c98ce1acd" xlink:to="loc_isba_InterestIncomeFederalFundsSoldAndOther_019eb325-4869-7f4b-9847-993c7ac2ebbc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncome_019eb325-4869-7ed0-9f10-04ebe759aae0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestIncome"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_NoninterestIncomeServiceChargesandFees_019eb325-4869-701d-876e-8fd95d59f57c" xlink:href="isba-20260630.xsd#isba_NoninterestIncomeServiceChargesandFees"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestIncome_019eb325-4869-7ed0-9f10-04ebe759aae0" xlink:to="loc_isba_NoninterestIncomeServiceChargesandFees_019eb325-4869-701d-876e-8fd95d59f57c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_NoninterestIncomeInvestmentAndTrustAdvisoryFees_019eb325-4869-7cb9-aa21-e69be5a1e3ce" xlink:href="isba-20260630.xsd#isba_NoninterestIncomeInvestmentAndTrustAdvisoryFees"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestIncome_019eb325-4869-7ed0-9f10-04ebe759aae0" xlink:to="loc_isba_NoninterestIncomeInvestmentAndTrustAdvisoryFees_019eb325-4869-7cb9-aa21-e69be5a1e3ce" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BankOwnedLifeInsuranceIncome_019eb325-4869-7378-bc7a-611c66a5f77a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BankOwnedLifeInsuranceIncome"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestIncome_019eb325-4869-7ed0-9f10-04ebe759aae0" xlink:to="loc_us-gaap_BankOwnedLifeInsuranceIncome_019eb325-4869-7378-bc7a-611c66a5f77a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfMortgageLoans_019eb325-4869-7b28-b485-aa27e58e5a58" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfMortgageLoans"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestIncome_019eb325-4869-7ed0-9f10-04ebe759aae0" xlink:to="loc_us-gaap_GainLossOnSaleOfMortgageLoans_019eb325-4869-7b28-b485-aa27e58e5a58" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncomeOtherOperatingIncome_019eb325-4869-7c41-b69f-f1ae0787caa3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestIncomeOtherOperatingIncome"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestIncome_019eb325-4869-7ed0-9f10-04ebe759aae0" xlink:to="loc_us-gaap_NoninterestIncomeOtherOperatingIncome_019eb325-4869-7c41-b69f-f1ae0787caa3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019eb325-4869-732f-bcae-d43b32b9ab48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-77bc-8c8e-6cb768715477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestAndDividendIncomeOperating"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestIncomeExpenseNet_019eb325-4869-732f-bcae-d43b32b9ab48" xlink:to="loc_us-gaap_InterestAndDividendIncomeOperating_019eb325-4869-77bc-8c8e-6cb768715477" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7330-9d1f-101a4ca363e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseOperating"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestIncomeExpenseNet_019eb325-4869-732f-bcae-d43b32b9ab48" xlink:to="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7330-9d1f-101a4ca363e7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7789-8f1c-8b41f51694ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseOperating"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDeposits_019eb325-4869-7793-9724-138f5e1d8e57" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseDeposits"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7789-8f1c-8b41f51694ae" xlink:to="loc_us-gaap_InterestExpenseDeposits_019eb325-4869-7793-9724-138f5e1d8e57" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase_019eb325-4869-75ae-8266-aefe091339e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7789-8f1c-8b41f51694ae" xlink:to="loc_us-gaap_InterestExpenseFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchase_019eb325-4869-75ae-8266-aefe091339e5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesShortTerm_019eb325-4869-75fa-a705-e0b462362897" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesShortTerm"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7789-8f1c-8b41f51694ae" xlink:to="loc_us-gaap_InterestExpenseFederalHomeLoanBankAndFederalReserveBankAdvancesShortTerm_019eb325-4869-75fa-a705-e0b462362897" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseSubordinatedNotesAndDebentures_019eb325-4869-7bf1-908c-ef6807990d78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseSubordinatedNotesAndDebentures"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpenseOperating_019eb325-4869-7789-8f1c-8b41f51694ae" xlink:to="loc_us-gaap_InterestExpenseSubordinatedNotesAndDebentures_019eb325-4869-7bf1-908c-ef6807990d78" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019eb325-4869-79e5-8ee7-18018edfcd8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_019eb325-4869-731b-8ae2-0a6a3b612c8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019eb325-4869-79e5-8ee7-18018edfcd8f" xlink:to="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_019eb325-4869-731b-8ae2-0a6a3b612c8d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncome_019eb325-4869-77cd-8410-09e7c2826a06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestIncome"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019eb325-4869-79e5-8ee7-18018edfcd8f" xlink:to="loc_us-gaap_NoninterestIncome_019eb325-4869-77cd-8410-09e7c2826a06" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpense_019eb325-4869-79f7-b557-404cf7481d8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpense"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019eb325-4869-79e5-8ee7-18018edfcd8f" xlink:to="loc_us-gaap_NoninterestExpense_019eb325-4869-79f7-b557-404cf7481d8e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_019eb325-4869-79c9-aebc-50d82ee6d9aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019eb325-4869-770d-9ca0-cc055884860d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_019eb325-4869-79c9-aebc-50d82ee6d9aa" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019eb325-4869-770d-9ca0-cc055884860d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses_019eb325-4869-76cc-99cd-6210f2ad597e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForLoanLeaseAndOtherLosses"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_019eb325-4869-79c9-aebc-50d82ee6d9aa" xlink:to="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses_019eb325-4869-76cc-99cd-6210f2ad597e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoninterestExpense"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019eb325-4869-75ae-9b93-4ad0bcb5b1f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019eb325-4869-75ae-9b93-4ad0bcb5b1f8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OccupancyNet_019eb325-4869-7190-85ef-5ef5210bc6cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OccupancyNet"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_OccupancyNet_019eb325-4869-7190-85ef-5ef5210bc6cb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalAndContractServicesExpense_019eb325-4869-7b91-91e2-60d6b934d4f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalAndContractServicesExpense"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_ProfessionalAndContractServicesExpense_019eb325-4869-7b91-91e2-60d6b934d4f3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_ATMandDebitCardExpense_019eb325-4869-7ffb-be51-6642190ab163" xlink:href="isba-20260630.xsd#isba_ATMandDebitCardExpense"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_isba_ATMandDebitCardExpense_019eb325-4869-7ffb-be51-6642190ab163" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketingExpense_019eb325-4869-7627-a1e2-2af2e02983a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketingExpense"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_MarketingExpense_019eb325-4869-7627-a1e2-2af2e02983a3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalDepositInsuranceCorporationPremiumExpense_019eb325-4869-77e1-8051-37ffc87d5f81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalDepositInsuranceCorporationPremiumExpense"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_FederalDepositInsuranceCorporationPremiumExpense_019eb325-4869-77e1-8051-37ffc87d5f81" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts_019f47b1-e450-710f-8256-3f0dbada07c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationIntegrationRelatedCosts"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_BusinessCombinationIntegrationRelatedCosts_019f47b1-e450-710f-8256-3f0dbada07c9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoninterestExpense_019eb325-4869-7e5b-aee2-a73f8ca96530" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNoninterestExpense"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NoninterestExpense_019eb325-4869-7b88-9634-50ba4c85863a" xlink:to="loc_us-gaap_OtherNoninterestExpense_019eb325-4869-7e5b-aee2-a73f8ca96530" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEUNAUDITED" xlink:type="simple" xlink:href="isba-20260630.xsd#INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEUNAUDITED"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEUNAUDITED" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb325-4869-7c27-8ecc-2f5df653c572" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_019eb325-4869-7cf3-9cfe-ebc75069b952" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb325-4869-7c27-8ecc-2f5df653c572" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax_019eb325-4869-7cf3-9cfe-ebc75069b952" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax_019eb325-4869-7d8d-9454-b31ea6f0ce31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb325-4869-7c27-8ecc-2f5df653c572" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax_019eb325-4869-7d8d-9454-b31ea6f0ce31" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019eb325-4869-7414-9e1e-6c0737837d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eb325-4869-7c18-a20d-105861a0dcb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTax_019eb325-4869-7414-9e1e-6c0737837d8a" xlink:to="loc_us-gaap_NetIncomeLoss_019eb325-4869-7c18-a20d-105861a0dcb0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb325-4869-7e24-b77d-b05455bf7a2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTax_019eb325-4869-7414-9e1e-6c0737837d8a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019eb325-4869-7e24-b77d-b05455bf7a2e" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED" xlink:type="simple" xlink:href="isba-20260630.xsd#INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/INTERIMCONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019eb325-4869-7456-89f5-0f2de5235bb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7ea7-8809-c611f19e6385" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019eb325-4869-7456-89f5-0f2de5235bb3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7ea7-8809-c611f19e6385" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-7dcc-99cd-1f9c96fba4e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019eb325-4869-7456-89f5-0f2de5235bb3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-7dcc-99cd-1f9c96fba4e8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7b8a-a31c-e8315a864f60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019eb325-4869-7456-89f5-0f2de5235bb3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7b8a-a31c-e8315a864f60" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_ProceedsFromSalesMaturitiesPrepaymentsAndCallsOfDebtSecuritiesAvailableForSale_019eb325-4869-77f5-83d6-61c69fdf09eb" xlink:href="isba-20260630.xsd#isba_ProceedsFromSalesMaturitiesPrepaymentsAndCallsOfDebtSecuritiesAvailableForSale"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_isba_ProceedsFromSalesMaturitiesPrepaymentsAndCallsOfDebtSecuritiesAvailableForSale_019eb325-4869-77f5-83d6-61c69fdf09eb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_019eb325-4869-7f57-9d35-911a6ed3ccb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_019eb325-4869-7f57-9d35-911a6ed3ccb0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromLoansAndLeases_019eb325-4869-70c2-903a-82029fb46bb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromLoansAndLeases"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_PaymentsForProceedsFromLoansAndLeases_019eb325-4869-70c2-903a-82029fb46bb8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019eb325-4869-78c4-b27e-591b8be1b2eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:calculationArc order="4" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019eb325-4869-78c4-b27e-591b8be1b2eb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireLifeInsurancePolicies_019eb325-4869-7b3a-84d2-e1bc4ecaedce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireLifeInsurancePolicies"/>
    <link:calculationArc order="5" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_PaymentsToAcquireLifeInsurancePolicies_019eb325-4869-7b3a-84d2-e1bc4ecaedce" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLifeInsurancePolicies_019eb325-4869-774b-9acf-912e9ef4390d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLifeInsurancePolicies"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_ProceedsFromLifeInsurancePolicies_019eb325-4869-774b-9acf-912e9ef4390d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfFederalHomeLoanBankStock_019eb325-4869-7a0a-8330-e3cc04c6bd88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfFederalHomeLoanBankStock"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_ProceedsFromSaleOfFederalHomeLoanBankStock_019eb325-4869-7a0a-8330-e3cc04c6bd88" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfForeclosedAssets_019eb325-4869-7eaf-90bf-77b63febbb8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfForeclosedAssets"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_ProceedsFromSaleOfForeclosedAssets_019eb325-4869-7eaf-90bf-77b63febbb8f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireOtherInvestments_019eb325-4869-7acd-9860-7a9b0c081d04" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireOtherInvestments"/>
    <link:calculationArc order="9" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019eb325-4869-721a-a070-f6802cba1035" xlink:to="loc_us-gaap_PaymentsToAcquireOtherInvestments_019eb325-4869-7acd-9860-7a9b0c081d04" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeposits_019eb325-4869-783c-9d73-ba2f8e273a18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInDeposits"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:to="loc_us-gaap_IncreaseDecreaseInDeposits_019eb325-4869-783c-9d73-ba2f8e273a18" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet_019eb325-4869-747c-9a04-599ae81b64a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:to="loc_us-gaap_IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet_019eb325-4869-747c-9a04-599ae81b64a2" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInLoansFromOtherFederalHomeLoanBanks_019eb325-4869-7f25-bd7e-016e9f9fff08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInLoansFromOtherFederalHomeLoanBanks"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:to="loc_us-gaap_IncreaseDecreaseInLoansFromOtherFederalHomeLoanBanks_019eb325-4869-7f25-bd7e-016e9f9fff08" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_019eb325-4869-7fae-b904-d7cc969087fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:calculationArc order="4" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_019eb325-4869-7fae-b904-d7cc969087fb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019eb325-4869-7c84-b382-49ab8fab900a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_019eb325-4869-7c84-b382-49ab8fab900a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_019eb325-4869-7dba-97d8-d6251d0ed0bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <link:calculationArc order="6" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019eb325-4869-7e98-b346-602e655ef86b" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_019eb325-4869-7dba-97d8-d6251d0ed0bd" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019eb325-4869-726d-9f6f-a5753f78e4c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_NetIncomeLoss_019eb325-4869-726d-9f6f-a5753f78e4c8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses_019eb325-4869-7f0d-be31-d6e6ca903061" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProvisionForLoanLeaseAndOtherLosses"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_ProvisionForLoanLeaseAndOtherLosses_019eb325-4869-7f0d-be31-d6e6ca903061" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019eb325-4869-7a4b-8b72-c6b8c8271f77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_Depreciation_019eb325-4869-7a4b-8b72-c6b8c8271f77" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium_019eb325-4869-7b26-893c-763bd73b6f70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium"/>
    <link:calculationArc order="4" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_InvestmentIncomeNetAmortizationOfDiscountAndPremium_019eb325-4869-7b26-893c-763bd73b6f70" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfMortgageLoans_019eb325-4869-7da9-8a4f-aab7081cae51" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfMortgageLoans"/>
    <link:calculationArc order="5" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_GainLossOnSaleOfMortgageLoans_019eb325-4869-7da9-8a4f-aab7081cae51" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_BankOwnedLifeInsuranceIncomeNetofExpense_019eb325-4869-7899-9249-eca939fd751f" xlink:href="isba-20260630.xsd#isba_BankOwnedLifeInsuranceIncomeNetofExpense"/>
    <link:calculationArc order="6" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_isba_BankOwnedLifeInsuranceIncomeNetofExpense_019eb325-4869-7899-9249-eca939fd751f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_GainLossOnRedemptionOfBankOwnedLifeInsurance_019eb325-4869-7c4e-8a7d-3fe529d9a429" xlink:href="isba-20260630.xsd#isba_GainLossOnRedemptionOfBankOwnedLifeInsurance"/>
    <link:calculationArc order="7" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_isba_GainLossOnRedemptionOfBankOwnedLifeInsurance_019eb325-4869-7c4e-8a7d-3fe529d9a429" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019eb325-4869-7b04-9131-1110a1983f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_ShareBasedCompensation_019eb325-4869-7b04-9131-1110a1983f5a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale_019eb325-4869-75ff-8de7-048b1466e9bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale"/>
    <link:calculationArc order="9" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_PaymentsForOriginationOfMortgageLoansHeldForSale_019eb325-4869-75ff-8de7-048b1466e9bd" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale_019eb325-4869-74b7-8129-d90bcae22529" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale"/>
    <link:calculationArc order="10" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_ProceedsFromSaleOfMortgageLoansHeldForSale_019eb325-4869-74b7-8129-d90bcae22529" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_019eb325-4869-7626-b5ed-6d23817d9e8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:calculationArc order="11" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_019eb325-4869-7626-b5ed-6d23817d9e8b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_019eb325-4869-77b2-bf5d-b94fbcfdfa08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherAccruedLiabilities"/>
    <link:calculationArc order="12" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019eb325-4869-7794-91ac-2192c3f93911" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherAccruedLiabilities_019eb325-4869-77b2-bf5d-b94fbcfdfa08" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/AFSSecuritiesAmortizedCostandFairValueofAFSSecuritieswithGrossUnrealizedGainsandLossesDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#AFSSecuritiesAmortizedCostandFairValueofAFSSecuritieswithGrossUnrealizedGainsandLossesDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/AFSSecuritiesAmortizedCostandFairValueofAFSSecuritieswithGrossUnrealizedGainsandLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7c6d-a713-e0b580f7716c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eb325-4869-75a9-8a06-a24b1270e0f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7c6d-a713-e0b580f7716c" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019eb325-4869-75a9-8a06-a24b1270e0f5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eb325-4869-7a6c-840a-b0a1b06dd96c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7c6d-a713-e0b580f7716c" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019eb325-4869-7a6c-840a-b0a1b06dd96c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-7b16-9539-a0b0fd6d14f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7c6d-a713-e0b580f7716c" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-7b16-9539-a0b0fd6d14f7" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/AFSSecuritiesAmortizedCostandFairValueofAFSSecuritiesbyContractualMaturityDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#AFSSecuritiesAmortizedCostandFairValueofAFSSecuritiesbyContractualMaturityDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/AFSSecuritiesAmortizedCostandFairValueofAFSSecuritiesbyContractualMaturityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-780c-8a0e-0a12c524ef09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue_019eb325-4869-702b-98e4-fdcaf31dd7ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-780c-8a0e-0a12c524ef09" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue_019eb325-4869-702b-98e4-fdcaf31dd7ce" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue_019eb325-4869-7c56-ab3f-6a71f4944c6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-780c-8a0e-0a12c524ef09" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue_019eb325-4869-7c56-ab3f-6a71f4944c6b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue_019eb325-4869-74cf-b5c5-ecf2ddeb0d20" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-780c-8a0e-0a12c524ef09" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue_019eb325-4869-74cf-b5c5-ecf2ddeb0d20" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue_019eb325-4869-7b87-b84a-227434cbe087" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-780c-8a0e-0a12c524ef09" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue_019eb325-4869-7b87-b84a-227434cbe087" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_AvailableforsaleSecuritiesWithVariableMonthlyPaymentsOrWithoutSingleMaturityDateFairValue_019eb325-4869-7d1a-8fc3-21d080c06600" xlink:href="isba-20260630.xsd#isba_AvailableforsaleSecuritiesWithVariableMonthlyPaymentsOrWithoutSingleMaturityDateFairValue"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019eb325-4869-780c-8a0e-0a12c524ef09" xlink:to="loc_isba_AvailableforsaleSecuritiesWithVariableMonthlyPaymentsOrWithoutSingleMaturityDateFairValue_019eb325-4869-7d1a-8fc3-21d080c06600" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7d85-ace9-648e6445e2aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis_019eb325-4869-7358-840b-8f2298c19ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7d85-ace9-648e6445e2aa" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis_019eb325-4869-7358-840b-8f2298c19ab1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveAmortizedCostBasis_019eb325-4869-7a6b-abcf-039d67af6581" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveAmortizedCostBasis"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7d85-ace9-648e6445e2aa" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveAmortizedCostBasis_019eb325-4869-7a6b-abcf-039d67af6581" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis_019eb325-4869-73e7-9cab-1e269e501abc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7d85-ace9-648e6445e2aa" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis_019eb325-4869-73e7-9cab-1e269e501abc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenAmortizedCostBasis_019eb325-4869-7ef0-a7db-f780a422b546" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenAmortizedCostBasis"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7d85-ace9-648e6445e2aa" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenAmortizedCostBasis_019eb325-4869-7ef0-a7db-f780a422b546" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_AvailableforsaleSecuritiesWithVariableMonthlyPaymentsOrWithoutSingleMaturityDateAmortizedCostBasis_019eb325-4869-73e3-a669-e6a4cb1c12bc" xlink:href="isba-20260630.xsd#isba_AvailableforsaleSecuritiesWithVariableMonthlyPaymentsOrWithoutSingleMaturityDateAmortizedCostBasis"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019eb325-4869-7d85-ace9-648e6445e2aa" xlink:to="loc_isba_AvailableforsaleSecuritiesWithVariableMonthlyPaymentsOrWithoutSingleMaturityDateAmortizedCostBasis_019eb325-4869-73e3-a669-e6a4cb1c12bc" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/AFSSecuritiesAFSSecuritieswithGrossUnrealizedLossesDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#AFSSecuritiesAFSSecuritieswithGrossUnrealizedLossesDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/AFSSecuritiesAFSSecuritieswithGrossUnrealizedLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019eb325-4869-738a-bafb-ebf6c0a3380b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019eb325-4869-70d0-8fdd-d2eec9d7d21b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019eb325-4869-738a-bafb-ebf6c0a3380b" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_019eb325-4869-70d0-8fdd-d2eec9d7d21b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019eb325-4869-7045-a901-582b61d6017d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_019eb325-4869-738a-bafb-ebf6c0a3380b" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_019eb325-4869-7045-a901-582b61d6017d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019eb325-4869-74fc-b134-14d87f69581c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions_019eb325-4869-7a72-ba5f-93b4d1528ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019eb325-4869-74fc-b134-14d87f69581c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions_019eb325-4869-7a72-ba5f-93b4d1528ae6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_019eb325-4869-7a7c-839c-f0e2547920fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_019eb325-4869-74fc-b134-14d87f69581c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions_019eb325-4869-7a7c-839c-f0e2547920fc" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/LoansandACLSummaryofCreditQualityIndicatorsbyYearofOriginationDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#LoansandACLSummaryofCreditQualityIndicatorsbyYearofOriginationDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/LoansandACLSummaryofCreditQualityIndicatorsbyYearofOriginationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff_019eb325-486a-7cde-8f76-668850184970" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff_019eb325-486a-7cde-8f76-668850184970" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff_019eb325-486a-7e6d-96a5-1ea3d01fd4c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff_019eb325-486a-7e6d-96a5-1ea3d01fd4c0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-7eab-beba-4198ac6fa2b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-7eab-beba-4198ac6fa2b7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-7313-adbf-494baa4270e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-7313-adbf-494baa4270e0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-7a8d-a8c5-5568bf0ee29e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-7a8d-a8c5-5568bf0ee29e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-70fa-b1f0-c8cee65d40ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff_019eb325-486a-70fa-b1f0-c8cee65d40ee" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff_019eb325-486a-7b4b-9570-9447cae02e4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff_019eb325-486a-7b4b-9570-9447cae02e4c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff_019eb325-486a-7ed0-a098-9fd911a64f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_019eb325-486a-745b-9be8-52024d1ac74a" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff_019eb325-486a-7ed0-a098-9fd911a64f5d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear_019eb325-486a-75d6-a817-2559e6ae52e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear_019eb325-486a-75d6-a817-2559e6ae52e3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear_019eb325-486a-7643-9397-d8d9573397be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear_019eb325-486a-7643-9397-d8d9573397be" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear_019eb325-486a-744b-bc2f-826cab32044c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear_019eb325-486a-744b-bc2f-826cab32044c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear_019eb325-486a-704b-be89-ebe00bc2529b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear_019eb325-486a-704b-be89-ebe00bc2529b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear_019eb325-486a-7872-8f8f-5cd6da20c941" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear_019eb325-486a-7872-8f8f-5cd6da20c941" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear_019eb325-486a-7011-b9c2-02360f928203" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear_019eb325-486a-7011-b9c2-02360f928203" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolving_019eb325-486a-79e7-9acc-416c23cd47b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolving"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolving_019eb325-486a-79e7-9acc-416c23cd47b3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan_019eb325-486a-7e76-88a4-0dbe0fc15729" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019eb325-486a-71a8-b3b0-66805da341c9" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan_019eb325-486a-7e76-88a4-0dbe0fc15729" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/LoansandACLSummaryofLoanModificationsbyPastDueStatusDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#LoansandACLSummaryofLoanModificationsbyPastDueStatusDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/LoansandACLSummaryofLoanModificationsbyPastDueStatusDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_isba_FinancingReceivableAllowanceForCreditLossPercent_019eb325-486a-71b0-83fa-942295ee4465" xlink:href="isba-20260630.xsd#isba_FinancingReceivableAllowanceForCreditLossPercent"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_FinancingReceivableAllowanceForCreditLossIndividuallyEvaluatedPercent_019eb325-486a-7b4c-b198-64f6780eafd0" xlink:href="isba-20260630.xsd#isba_FinancingReceivableAllowanceForCreditLossIndividuallyEvaluatedPercent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_isba_FinancingReceivableAllowanceForCreditLossPercent_019eb325-486a-71b0-83fa-942295ee4465" xlink:to="loc_isba_FinancingReceivableAllowanceForCreditLossIndividuallyEvaluatedPercent_019eb325-486a-7b4c-b198-64f6780eafd0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_FinancingReceivableAllowanceForCreditLossCollectivelyEvaluatedPercent_019eb325-486a-704f-8930-4b851fdda686" xlink:href="isba-20260630.xsd#isba_FinancingReceivableAllowanceForCreditLossCollectivelyEvaluatedPercent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_isba_FinancingReceivableAllowanceForCreditLossPercent_019eb325-486a-71b0-83fa-942295ee4465" xlink:to="loc_isba_FinancingReceivableAllowanceForCreditLossCollectivelyEvaluatedPercent_019eb325-486a-704f-8930-4b851fdda686" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019eb325-486a-79cf-ad55-9f3ace572a85" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1_019eb325-486a-72b1-b57c-81426b1d64aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019eb325-486a-79cf-ad55-9f3ace572a85" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1_019eb325-486a-72b1-b57c-81426b1d64aa" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment_019eb325-486a-7ad6-bbf7-02a8d05b4237" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_019eb325-486a-79cf-ad55-9f3ace572a85" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment_019eb325-486a-7ad6-bbf7-02a8d05b4237" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/BorrowedFundsPledgedFinancialInstrumentsDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#BorrowedFundsPledgedFinancialInstrumentsDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/BorrowedFundsPledgedFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_isba_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesAndLoansReceivablePledgedAsCollateral_019eb325-486a-7153-803c-4bb27e00a567" xlink:href="isba-20260630.xsd#isba_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesAndLoansReceivablePledgedAsCollateral"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_019eb325-486a-703e-8d02-18cb25b0df24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_isba_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesAndLoansReceivablePledgedAsCollateral_019eb325-486a-7153-803c-4bb27e00a567" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_019eb325-486a-703e-8d02-18cb25b0df24" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseFairValueOfCollateral_019eb325-486a-77e3-8cbd-e6b436f7af2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseFairValueOfCollateral"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_isba_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesAndLoansReceivablePledgedAsCollateral_019eb325-486a-7153-803c-4bb27e00a567" xlink:to="loc_us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseFairValueOfCollateral_019eb325-486a-77e3-8cbd-e6b436f7af2d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositLiabilitiesCollateralIssuedFinancialInstruments_019eb325-486a-742b-b543-3da03f171448" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepositLiabilitiesCollateralIssuedFinancialInstruments"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_isba_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesAndLoansReceivablePledgedAsCollateral_019eb325-486a-7153-803c-4bb27e00a567" xlink:to="loc_us-gaap_DepositLiabilitiesCollateralIssuedFinancialInstruments_019eb325-486a-742b-b543-3da03f171448" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/ComputationofEarningsPerCommonShareScheduleofEarningsPerShareDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#ComputationofEarningsPerCommonShareScheduleofEarningsPerShareDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/ComputationofEarningsPerCommonShareScheduleofEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019eb325-486a-7f79-b205-d2eb5bf232a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019eb325-486a-7fce-a33f-daa890cfc16e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019eb325-486a-7f79-b205-d2eb5bf232a1" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019eb325-486a-7fce-a33f-daa890cfc16e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019eb325-486a-7554-b126-5b99042ca617" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019eb325-486a-7f79-b205-d2eb5bf232a1" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019eb325-486a-7554-b126-5b99042ca617" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/CapitalRatiosandShareholdersEquityChangesinAOCIbyComponentsDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#CapitalRatiosandShareholdersEquityChangesinAOCIbyComponentsDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/CapitalRatiosandShareholdersEquityChangesinAOCIbyComponentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_019eb325-486a-7cd5-8cce-6f142fb040e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_019eb325-486a-7562-abab-b9973e623f31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_019eb325-486a-7cd5-8cce-6f142fb040e5" xlink:to="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_019eb325-486a-7562-abab-b9973e623f31" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_019eb325-486a-745f-b59b-3ef73943373c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent_019eb325-486a-7cd5-8cce-6f142fb040e5" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_019eb325-486a-745f-b59b-3ef73943373c" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.isabellabank.com/role/FairValueRecordedAmountofAssetsandLiabilitiesMeasuredatFairValueDetails" xlink:type="simple" xlink:href="isba-20260630.xsd#FairValueRecordedAmountofAssetsandLiabilitiesMeasuredatFairValueDetails"/>
  <link:calculationLink xlink:role="http://www.isabellabank.com/role/FairValueRecordedAmountofAssetsandLiabilitiesMeasuredatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019fa907-c7a0-7409-a39c-8a11be002a47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fa908-2520-7b71-ac17-5467d4d29589" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsFairValueDisclosure_019fa907-c7a0-7409-a39c-8a11be002a47" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019fa908-2520-7b71-ac17-5467d4d29589" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_ImpairedFinancingReceivableFairValueDisclosure_019fa908-8ce8-7915-998e-74f9611e1e46" xlink:href="isba-20260630.xsd#isba_ImpairedFinancingReceivableFairValueDisclosure"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsFairValueDisclosure_019fa907-c7a0-7409-a39c-8a11be002a47" xlink:to="loc_isba_ImpairedFinancingReceivableFairValueDisclosure_019fa908-8ce8-7915-998e-74f9611e1e46" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_OtherMortgageServicingRightsFairValueDisclosure_019fa908-dcaa-7b03-81fe-7d833e5efbc0" xlink:href="isba-20260630.xsd#isba_OtherMortgageServicingRightsFairValueDisclosure"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsFairValueDisclosure_019fa907-c7a0-7409-a39c-8a11be002a47" xlink:to="loc_isba_OtherMortgageServicingRightsFairValueDisclosure_019fa908-dcaa-7b03-81fe-7d833e5efbc0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_isba_ForeclosedAssetsFairValueDisclosure_019fa909-2439-7cc3-b896-cf32326bd82d" xlink:href="isba-20260630.xsd#isba_ForeclosedAssetsFairValueDisclosure"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="https://xbrl.org/2023/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsFairValueDisclosure_019fa907-c7a0-7409-a39c-8a11be002a47" xlink:to="loc_isba_ForeclosedAssetsFairValueDisclosure_019fa909-2439-7cc3-b896-cf32326bd82d" xlink:type="arc"/>
  </link:calculationLink>
</link:linkbase>
