Significant Accounting Policies	6 Months Ended
Jun. 30, 2026
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Basis of Presentation and Consolidation The consolidated financial statements include the accounts of Isabella Bank Corporation, a registered financial holding company, and its wholly owned banking subsidiary, Isabella Bank. All intercompany balances and accounts have been eliminated in consolidation. References to “we,” “our,” “us,” and “the Corporation” refer to Isabella Bank Corporation, a Michigan corporation and registered financial holding company, our wholly-owned banking subsidiary, Isabella Bank, and our other consolidated subsidiaries. References to “the Bank” refer to Isabella Bank. The accompanying unaudited interim condensed consolidated financial statements in this Form 10-Q have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In our opinion, all adjustments considered necessary for a fair presentation have been included. Operating results for the three and six-month periods ended June 30, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026. For further information, refer to our Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on March 13, 2026 (the “2025 Annual Report on Form 10-K”). All financial data presented in these notes, as well as in Management’s Discussion and Analysis of Financial Condition and Results of Operations of this Form 10-Q, including financial data presented in the tables and explanations thereof, are expressed in thousands except per share amounts and ratios and unless otherwise noted. Recent Developments On June 16, 2026, the Corporation and the Bank entered into an equity distribution agreement with Piper Sandler & Co., as sales agent, pursuant to which the Corporation may offer and sell, from time to time, shares of its common stock with an aggregate gross sales price of up to $30.0 million, including through “at-the-market” offerings and other permitted methods. The sales agent is entitled to a commission of up to 3.0% of the gross sales price of the common stock sold in such offering. The Corporation is not obligated to sell any shares of its common stock pursuant to the equity distribution agreement, and may suspend or terminate sales thereunder at any time. Any shares sold will be issued pursuant to the Corporation’s effective shelf registration statement on Form S-3 and related prospectus supplement, and net proceeds, if any, are expected to be used for general corporate purposes, which may include, without limitation, contribution to the capital of the Bank to support its lending activities and growth. Please see Note 5 below for additional information about our at-the-market offering. On June 11, 2026, the Corporation, 401 Merger Sub, Inc., a Michigan corporation and a wholly owned subsidiary of the Corporation (“Merger Sub”), and Grand River Commerce, Inc. (“Grand River”), entered into an Agreement and Plan of Merger (the “Merger Agreement”). The Merger Agreement provides that, upon the terms and subject to the conditions set forth therein, Merger Sub will merge with and into Grand River, with Grand River as the surviving entity (the “Merger”), and immediately following the Merger, Grand River will merge with and into the Corporation, with the Corporation as the surviving entity (the “Second Step Merger”). The Merger Agreement further provides that immediately following the Second Step Merger, Grand River Bank, a Michigan state-chartered member bank and wholly owned subsidiary of Grand River, will merge with and into the Bank, with the Bank as the surviving bank (the “Bank Merger” and, together with the Merger and the Second Step Merger, the “Transaction”). We expect to complete the Merger in the fourth quarter of 2026, subject to satisfaction of closing conditions, including receipt of customary required regulatory approvals and the approval of the Merger Agreement by the shareholders of Grand River. Upon the terms and subject to the conditions of the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each voting and non-voting share of common stock of Grand River (“Grand River Common Stock”) issued and outstanding immediately prior to the Effective Time, other than certain shares held by Grand River or the Corporation or dissenting shares, will be converted into the right to receive, at the election of the holder thereof, and subject to adjustment and proration, as applicable, (i) an amount of cash equal to the quotient of (A) $18,262,391 (the “Aggregate Cash Consideration”), divided by (B) the product obtained by multiplying (x) the number of shares of Grand River Common Stock issued and outstanding as of the Effective Time by (y) 0.35 (the “Cash Conversion Number”), rounded to the nearest cent (the “Per Share Cash Consideration”), or (ii) the number of shares of common stock of the Corporation, no par value (“Isabella Common Stock”), multiplied by the Exchange Ratio (as defined below). The Exchange Ratio is defined in the Merger Agreement as a number, as adjusted, of shares of Isabella Common Stock equal to the quotient of (A) 839,003 shares of Isabella Common Stock, divided by (B) the difference of (1) the aggregate number of shares of Grand River Common Stock issued and outstanding immediately prior to the Effective Time, other than certain shares held by Grand River or the Corporation or dissenting shares, minus (2) the Cash Conversion Number, rounded to the nearest ten thousandth (the “Per Share Stock Consideration”). The Per Share Cash Consideration and/or the Per Share Stock Consideration are sometimes referred to herein collectively as the “Merger Consideration.” Merger Consideration elections by Grand River shareholders will be subject to proration procedures whereby 65% of the shares of Grand River Common Stock will be exchanged for the Per Share Stock Consideration and 35% of the shares of Grand River common stock will be exchanged for the Per Share Cash Consideration. Based on the assumption of 9,136,529 shares of Grand River Common Stock issued and outstanding as of the Effective Time, the Per Share Cash Consideration to be paid is estimated to be approximately $5.71 and the Exchange Ratio is estimated to be approximately 0.1413. At March 31, 2026, Grand River had approximately $511.7 million in total assets, $433.0 million in total loans and $438.9 million in total deposits. The pro forma company is projected to have approximately $2.7 billion in total assets. Identification and Classification of Merger-Related Expenses Merger-related expenses are costs incurred directly in connection with merger and acquisition activities and are expensed in the period in which the costs are incurred and services are received. The costs to issue equity securities associated with the Merger are netted against the value of the securities issued. Merger-related expenses are expected to include legal fees for negotiation and drafting of merger agreements, accounting and auditing fees related to due diligence and financial statement preparation, consulting fees for strategic advisory services specific to the merger, costs related to regulatory filings and compliance, expenses for integration planning and execution (including IT, systems integration, and contract terminations), severance and retention bonuses for employees affected by the Merger, and travel and accommodation expenses directly related to merger activities. Merger-related expenses of $505,000 recognized in second quarter 2026 primarily include consulting fees and legal fees. Operating Segments Segment information is prepared on the same basis that our Chief Executive Officer, who is our Chief Operating Decision Maker (“CODM”), manages our segments, evaluates financial results, and makes key operating decisions. While the CODM monitors the revenue streams of our various products and services, operations are managed, and financial performance is evaluated on a corporate-wide basis. Operating segments are aggregated into one as operating results for all segments are similar. Accordingly, all of the banking-related operations are considered by management to be aggregated in one reportable operating segment. The segment is also distinguished by the level of information provided to the CODM, who uses such information to review performance of various components of the business, which are then aggregated if operating performance, products and services, and geographical regions are similar. The CODM will evaluate the financial performance of our business components by evaluating revenue streams, significant expenses, and budget to actual results in assessing our reportable segment and in the determination of allocating resources. Further, the CODM uses revenue streams to evaluate product pricing and significant expenses to assess performance and evaluate return on assets. Consolidated net income is used to benchmark our results against our competitors. Benchmarking and monitoring of budget to actual results are used in assessing performance and in establishing compensation. Revenue from banking operations consists primarily of loan and investment interest, deposit related fees, and wealth fees. Interest expense, provision for credit losses, compensation, and occupancy and equipment costs provide the significant expenses in our banking operations. All operations are domestic. Changes in Significant Accounting Policies Our accounting policies are materially the same as those discussed in Note 1 to the Consolidated Financial Statements included in our 2025 Annual Report on Form 10-K. Subsequent Events We evaluated subsequent events after June 30, 2026 through the date our interim condensed consolidated financial statements were issued for potential recognition and disclosure. Management determined that no subsequent events require financial statement recognition or disclosure between June 30, 2026 and the date our interim condensed consolidated financial statements were issued. Pending Accounting Standards ASU No. 2024-03: “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses” In November 2024, ASU No. 2024-03 was issued to improve the disclosures about a public business entity’s expenses and address requests from investors for more detailed information about the types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions (such as cost of sales, selling general and administrative expense, and research and development). The new authoritative guidance is effective for annual periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027, as clarified in ASU No. 2025-01 issued in January 2025. The new authoritative guidance under ASU No. 2024-03 is not expected to have a significant impact on our operations or financial statement disclosures.

The consolidated financial statements include the accounts of Isabella Bank Corporation, a registered financial holding company, and its wholly owned banking subsidiary, Isabella Bank. All intercompany balances and accounts have been eliminated in consolidation. References to “we,” “our,” “us,” and “the Corporation” refer to Isabella Bank Corporation, a Michigan corporation and registered financial holding company, our wholly-owned banking subsidiary, Isabella Bank, and our other consolidated subsidiaries. References to “the Bank” refer to Isabella Bank.

The accompanying unaudited interim condensed consolidated financial statements in this Form 10-Q have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In our opinion, all adjustments considered necessary for a fair presentation have been included. Operating results for the three and six-month periods ended June 30, 2026 are not necessarily indicative of the results that may be expected for the year ending December 31, 2026. For further information, refer to our Annual Report on Form 10-K for the year ended December 31, 2025, as filed with the SEC on March 13, 2026 (the “2025 Annual Report on Form 10-K”). All financial data presented in these notes, as well as in Management’s Discussion and Analysis of Financial Condition and Results of Operations of this Form 10-Q, including financial data presented in the tables and explanations thereof, are expressed in thousands except per share amounts and ratios and unless otherwise noted.

On June 16, 2026, the Corporation and the Bank entered into an equity distribution agreement with Piper Sandler & Co., as sales agent, pursuant to which the Corporation may offer and sell, from time to time, shares of its common stock with an aggregate gross sales price of up to $30.0 million, including through “at-the-market” offerings and other permitted methods. The sales agent is entitled to a commission of up to 3.0% of the gross sales price of the common stock sold in such offering. The Corporation is not obligated to sell any shares of its common stock pursuant to the equity distribution agreement, and may suspend or terminate sales thereunder at any time. Any shares sold will be issued pursuant to the Corporation’s effective shelf registration statement on Form S-3 and related prospectus supplement, and net proceeds, if any, are expected to be used for general corporate purposes, which may include, without limitation, contribution to the capital of the Bank to support its lending activities and growth. Please see Note 5 below for additional information about our at-the-market offering.

On June 11, 2026, the Corporation, 401 Merger Sub, Inc., a Michigan corporation and a wholly owned subsidiary of the Corporation (“Merger Sub”), and Grand River Commerce, Inc. (“Grand River”), entered into an Agreement and Plan of Merger (the “Merger Agreement”). The Merger Agreement provides that, upon the terms and subject to the conditions set forth therein, Merger Sub will merge with and into Grand River, with Grand River as the surviving entity (the “Merger”), and immediately following the Merger, Grand River will merge with and into the Corporation, with the Corporation as the surviving entity (the “Second Step Merger”). The Merger Agreement further provides that immediately following the Second Step Merger, Grand River Bank, a Michigan state-chartered member bank and wholly owned subsidiary of Grand River, will merge with and into the Bank, with the Bank as the surviving bank (the “Bank Merger” and, together with the Merger and the Second Step Merger, the “Transaction”). We expect to complete the Merger in the fourth quarter of 2026, subject to satisfaction of closing conditions, including receipt of customary required regulatory approvals and the approval of the Merger Agreement by the shareholders of Grand River.

Upon the terms and subject to the conditions of the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each voting and non-voting share of common stock of Grand River (“Grand River Common Stock”) issued and outstanding immediately prior to the Effective Time, other than certain shares held by Grand River or the Corporation or dissenting shares, will be converted into the right to receive, at the election of the holder thereof, and subject to adjustment and proration, as applicable, (i) an amount of cash equal to the quotient of (A) $18,262,391 (the “Aggregate Cash Consideration”), divided by (B) the product obtained by multiplying (x) the number of shares of Grand River Common Stock issued and outstanding as of the Effective Time by (y) 0.35 (the “Cash Conversion Number”), rounded to the nearest cent (the “Per Share Cash Consideration”), or (ii) the number of shares of common stock of the Corporation, no par value (“Isabella Common Stock”), multiplied by the Exchange Ratio (as defined below).

The Exchange Ratio is defined in the Merger Agreement as a number, as adjusted, of shares of Isabella Common Stock equal to the quotient of (A) 839,003 shares of Isabella Common Stock, divided by (B) the difference of (1) the aggregate number of shares of Grand River Common Stock issued and outstanding immediately prior to the Effective Time, other than certain shares held by Grand River or the Corporation or dissenting shares, minus (2) the Cash Conversion Number, rounded to the nearest ten

Merger Consideration elections by Grand River shareholders will be subject to proration procedures whereby 65% of the shares of Grand River Common Stock will be exchanged for the Per Share Stock Consideration and 35% of the shares of Grand River common stock will be exchanged for the Per Share Cash Consideration. Based on the assumption of 9,136,529 shares of Grand River Common Stock issued and outstanding as of the Effective Time, the Per Share Cash Consideration to be paid is estimated to be approximately $5.71 and the Exchange Ratio is estimated to be approximately 0.1413. At March 31, 2026, Grand River had approximately $511.7 million in total assets, $433.0 million in total loans and $438.9 million in total deposits. The pro forma company is projected to have approximately $2.7 billion in total assets.

Merger-related expenses are costs incurred directly in connection with merger and acquisition activities and are expensed in the period in which the costs are incurred and services are received. The costs to issue equity securities associated with the Merger are netted against the value of the securities issued. Merger-related expenses are expected to include legal fees for negotiation and drafting of merger agreements, accounting and auditing fees related to due diligence and financial statement preparation, consulting fees for strategic advisory services specific to the merger, costs related to regulatory filings and compliance, expenses for integration planning and execution (including IT, systems integration, and contract terminations), severance and retention bonuses for employees affected by the Merger, and travel and accommodation expenses directly related to merger activities. Merger-related expenses of $505,000 recognized in second quarter 2026 primarily include consulting fees and legal fees.

Segment information is prepared on the same basis that our Chief Executive Officer, who is our Chief Operating Decision Maker (“CODM”), manages our segments, evaluates financial results, and makes key operating decisions. While the CODM monitors the revenue streams of our various products and services, operations are managed, and financial performance is evaluated on a corporate-wide basis. Operating segments are aggregated into one as operating results for all segments are similar. Accordingly, all of the banking-related operations are considered by management to be aggregated in one reportable operating segment.

The segment is also distinguished by the level of information provided to the CODM, who uses such information to review performance of various components of the business, which are then aggregated if operating performance, products and services, and geographical regions are similar. The CODM will evaluate the financial performance of our business components by evaluating revenue streams, significant expenses, and budget to actual results in assessing our reportable segment and in the determination of allocating resources. Further, the CODM uses revenue streams to evaluate product pricing and significant expenses to assess performance and evaluate return on assets.

Consolidated net income is used to benchmark our results against our competitors. Benchmarking and monitoring of budget to actual results are used in assessing performance and in establishing compensation. Revenue from banking operations consists primarily of loan and investment interest, deposit related fees, and wealth fees. Interest expense, provision for credit losses, compensation, and occupancy and equipment costs provide the significant expenses in our banking operations. All operations are domestic.

We evaluated subsequent events after June 30, 2026 through the date our interim condensed consolidated financial statements were issued for potential recognition and disclosure. Management determined that no subsequent events require financial statement recognition or disclosure between June 30, 2026 and the date our interim condensed consolidated financial statements were issued.

In November 2024, ASU No. 2024-03 was issued to improve the disclosures about a public business entity’s expenses and address requests from investors for more detailed information about the types of expenses (including purchases of inventory, employee compensation, depreciation, amortization, and depletion) in commonly presented expense captions (such as cost of sales, selling general and administrative expense, and research and development). The new authoritative guidance is effective for annual periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027, as clarified in ASU No. 2025-01 issued in January 2025. The new authoritative guidance under ASU No. 2024-03 is not expected to have a significant impact on our operations or financial statement disclosures.