Summary of Significant Accounting Policies (Policies)	6 Months Ended
Dec. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Consolidation and Presentation	Basis of consolidation and presentation The consolidated financial statements include the accounts of the Company, its wholly owned subsidiary Winchester Savings Bank (the “Bank”) and the Bank's wholly owned subsidiaries, Sachem Holdings, Inc., Aberjona Holdings, Inc., 1871 Company, LLC, and Wedgemere Holdings, LLC. Sachem Holdings, Inc. and Aberjona Holdings, Inc. function as Massachusetts security corporations that buy, sell and hold securities. 1871 Company, LLC's principal activity is holding of bank premises. Wedgemere Holdings, LLC's principal activity is the holding of properties acquired in settlement of loans. All significant intercompany balances and transactions have been eliminated in consolidation.
Business	Business The Company is a Maryland corporation whose primarily purpose is to act as the holding company for the Bank. The Bank provides a variety of financial services to individuals and small businesses through its offices in Winchester, Woburn, Danvers and Arlington, Massachusetts. Its primary deposit products are checking, savings and term certificate accounts and its primary lending products are residential, commercial and multi-family real estate and construction loans.
Reorganization	Reorganization On December 4, 2024, the Board of Trustees of the Bank adopted a plan of reorganization from a Mutual Savings Bank to a Mutual Holding Company and Plan of Stock Issuance (the "Plan"). The Plan received the required approvals of various regulatory agencies. The Bank’s reorganization and the related stock offering of the Company were consummated on April 30, 2025. The Company sold 3,997,012 shares of common stock at $10.00 per share for gross proceeds of $39,970,000. In connection with the reorganization, the Company also issued 5,112,457 shares of common stock to Winchester Bancorp, MHC, the Company’s mutual holding company parent, and issued 185,907 shares of common stock to the Winchester Savings Bank Charitable Foundation, Inc. A liquidation account was established by Winchester Bancorp, Inc. for the benefit of eligible account holders equal to the percentage of the shares of common stock issued in the offering to persons other than Winchester Bancorp, MHC multiplied by the net worth of Winchester Savings Bank as of September 30, 2024. In the unlikely event of a complete liquidation of (i) the Bank or (ii) the Bank and the Company, all claims of creditors, including those of depositors, will be paid first. However, except with respect to the liquidation account to be established, a depositor’s claim would be solely for the principal amount of his or her deposit accounts plus accrued interest. Depositors generally would not have an interest in the value of the assets of Winchester Savings Bank or Winchester Bancorp, Inc. above that amount. On any June 30 annual closing date, if the amount in any applicable deposit account is less than the amount in the deposit account as of the close of business on November 30, 2023, or any other annual closing date, then the liquidation account as well as the interest in the liquidation account relating to such deposit account would be reduced from time to time by the proportion of any such reduction, and such interest will cease to exist if such deposit account is closed. In addition, no interest in the liquidation account would ever be increased despite any subsequent increase in the related deposit account.
Use of Estimates	Use of estimates In preparing consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the consolidated balance sheet and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The allowance for credit losses is a material estimate that is particularly susceptible to significant change in the near term.
Fair Value Hierarchy	Fair value hierarchy The Company groups its assets and liabilities measured at fair value in three levels, based on the markets in which the assets are traded and the reliability of the assumptions used to determine fair value. Level 1 – Valuation is based on quoted prices in active markets for identical assets. Valuations are obtained from readily available pricing sources for market transactions involving identical assets. Level 2 – Valuation is based on observable inputs other than Level 1 prices, such as quoted prices for similar assets; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets. Level 3 – Valuation is based on unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets. Level 3 assets include financial instruments whose value is determined using unobservable inputs to pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation. Defined benefit pension plan investments in hedge funds are measured using the net asset value per share (or its equivalent) as a practical expedient and have not been classified in the fair value hierarchy.
Accrued Interest Receivable	Accrued Interest Receivable The Company elected not to measure an allowance for credit losses for accrued interest receivable and instead elected to reverse interest income on loans or securities that are placed on nonaccrual status, which is generally when the instrument is 90 days past due, or earlier if the Company believes the collection of interest is doubtful. The Company has concluded that this policy results in the timely reversal of uncollectible interest.
Allowance for Credit Losses-Loans	Allowance for Credit Losses-Loans The allowance for credit losses is evaluated on a regular basis by management. This evaluation is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available. For the year ended June 30, 2025, the Company measured the allowance for credit losses using the Scaled CECL Allowance for Losses Estimator (“SCALE”) which has asset size limitations for institutions to use the methodology. Effective July 1, 2025 the Company could not longer use SCALE and changed its Allowance for Credit Loss methodology to use a quantitative Discounted Cash Flow (“DCF”) model combined with the assessment of certain qualitative factors. Collectively evaluated loans The allowance for credit losses is established based upon the Company's current estimate of expected lifetime credit losses on loans measured at amortized cost. Credit losses are charged against the allowance when management's assessments confirm that the Company will not collect the full amortized cost basis of a loan. Subsequent recoveries, if any, are credited to the allowance. The Company estimates credit losses for financial assets on a collective basis for loans sharing similar risk characteristics. The Company segments financial assets with similar risk characteristics and has elected to segment its loans based on Federal Call codes used for reporting loans to the Federal Deposit Insurance Corporation as part of the Call Report process. These segments are collectively evaluated for expected credit losses using a quantitative DCF model combined with an assessment of certain qualitative factors designed to address forecast risk and model risk inherent in the quantitative model output. The Company has elected to use this approach because DCF models allow for effective incorporation of a reasonable and supportable forecast in a directionally consistent and objective manner and peer data is available for certain inputs such as the probability of default and the loss given default. The quantitative model utilizes a loss factor based approach to estimate expected credit losses, which are derived from industry peer loss experience. The model estimates expected credit losses using loan level data over the estimated life of the exposure, considering the effect of prepayments. Economic forecasts are incorporated into the estimate over a reasonable and supportable forecast period, beyond which is a reversion to the historical long-run average using the straight-line reversion method. Management periodically evaluates a reasonable and supportable forecast period and a reversion period to be appropriate for purposes of estimating expected credit losses. The qualitative risk factors impacting the expected risk of loss within the portfolio include the following: • changes in the Company’s loan policies, procedures and strategies; • changes in international, national, regional, and local economic and business conditions; • changes in the nature and volume of the portfolio and terms of loans; • changes in experience, depth, and ability of lending management; • changes in the volume, trend, and severity of past due financial assets; • changes in the quality of the organization’s loan review system; • changes in the value of underlying collateral for collateral-dependent loans; • the existence and effect of any concentrations of credit, and changes in the level of such concentrations; and • the effect of competition and legal/regulatory requirements on the portfolio. Individually Evaluated Loans Loans that do not share similar risk characteristics with any pools of assets are subject to individual evaluation and are removed from the collectively assessed pools to avoid double counting. This includes loans on non-accrual and loans that are 90 days or greater past due. For the loans that will be individually evaluated, the Company will use either a discounted cash flow ("DCF") approach or a fair value of collateral approach. The latter approach will be used for loans that are collateral dependent, that is, when the borrower is experiencing financial difficulty and repayment is expected to be provided substantially through the operation or sale of the collateral, expected credit losses are based on fair value of the collateral at the reporting date, adjusted for selling costs as appropriate. Unallocated component An unallocated component may be maintained to cover uncertainties that could affect management’s estimate of probable losses. The unallocated portion of the allowance reflects the margin of imprecision inherent in the underlying assumptions used in the methodologies for estimating collectively and individually evaluated loans in the portfolio.
Allowance for Credit Losses- Off-Balance Sheet Credit Exposures	Allowance for Credit Losses- Off-Balance Sheet Credit Exposures The Company has off-balance sheet financial instruments, which include commitments to extend credit, standby letters of credit and commercial letters of credit. The Company estimates expected credit losses over the contractual period in which the Company is exposed to risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company. The Company’s allowance for credit losses on off-balance sheet credit exposures is recognized as a liability in accrued expenses and other liabilities on the consolidated balance sheets, with adjustments to the reserve recognized in the provision for credit losses in the consolidated statements of operations. The credit risk associated with these commitments is evaluated in a manner similar to the allowance for credit losses on loans with an additional assumption of probability of funding.
Derivatives and Hedging	Derivatives and Hedging The Company follows Accounting Standards Codification (“ASC”) Topic 815, Derivatives and Hedging, with regard to disclosure requirements for derivatives and hedging activities, with the intent to provide users of financial statements with an enhanced understanding of: (a) how and why an entity uses derivative instruments, (b) how the entity accounts for derivative instruments and related hedged items, and (c) how derivative instruments and related hedged items affect an entity’s financial position and performance. Qualitative disclosures explain the Company’s objectives and strategies for using derivatives, and quantitative disclosures are made regarding the fair value of, and gains and losses on, derivative instruments, and about credit-risk-related contingent features in derivative instruments. As required by ASC 815, the Company reports all derivatives on its balance sheet at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting, and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. Derivatives designated and qualifying as a hedge of the exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. Derivatives designated and qualifying as a hedge of the exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. In a fair value hedge, hedge accounting generally provides for the matching of the timing of gain or loss recognition on the hedging instrument with the recognition of the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk.
Recent Accounting Pronouncements	Recent accounting pronouncements Management has not identified any Accounting Standards Updates that have been issued but are not yet effective and could have a significant impact on the Company’s financial reporting or disclosure requirements.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Dec. 31, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of consolidation and presentation

The consolidated financial statements include the accounts of the Company, its wholly owned subsidiary Winchester Savings Bank (the “Bank”) and the Bank's wholly owned subsidiaries, Sachem Holdings, Inc., Aberjona Holdings, Inc., 1871 Company, LLC, and Wedgemere Holdings, LLC. Sachem Holdings, Inc. and Aberjona Holdings, Inc. function as Massachusetts security corporations that buy, sell and hold securities. 1871 Company, LLC's principal activity is holding of bank premises. Wedgemere Holdings, LLC's principal activity is the holding of properties acquired in settlement of loans.

All significant intercompany balances and transactions have been eliminated in consolidation.

Business

The Company is a Maryland corporation whose primarily purpose is to act as the holding company for the Bank. The Bank provides a variety of financial services to individuals and small businesses through its offices in Winchester, Woburn, Danvers and Arlington, Massachusetts. Its primary deposit products are checking, savings and term certificate accounts and its primary lending products are residential, commercial and multi-family real estate and construction loans.

Reorganization

On December 4, 2024, the Board of Trustees of the Bank adopted a plan of reorganization from a Mutual Savings Bank to a Mutual Holding Company and Plan of Stock Issuance (the "Plan"). The Plan received the required approvals of various regulatory agencies. The Bank’s reorganization and the related stock offering of the Company were consummated on April 30, 2025. The Company sold 3,997,012 shares of common stock at $10.00 per share for gross proceeds of $39,970,000. In connection with the reorganization, the Company also issued 5,112,457 shares of common stock to Winchester Bancorp, MHC, the Company’s mutual holding company parent, and issued 185,907 shares of common stock to the Winchester Savings Bank Charitable Foundation, Inc.

A liquidation account was established by Winchester Bancorp, Inc. for the benefit of eligible account holders equal to the percentage of the shares of common stock issued in the offering to persons other than Winchester Bancorp, MHC multiplied by the net worth of Winchester Savings Bank as of September 30, 2024. In the unlikely event of a complete liquidation of (i) the Bank or (ii) the Bank and the Company, all claims of creditors, including those of depositors, will be paid first. However, except with respect to the liquidation account to be established, a depositor’s claim would be solely for the principal amount of his or her deposit accounts plus accrued interest. Depositors generally would not have an interest in the value of the assets of Winchester Savings Bank or Winchester Bancorp, Inc. above that amount. On any June 30 annual closing date, if the amount in any applicable deposit account is less than the amount in the deposit account as of the close of business on November 30, 2023, or any other annual closing date, then the liquidation account as well as the interest in the liquidation account relating to such deposit account would be reduced from time to time by the proportion of any such reduction, and such interest will cease to exist if such deposit account is closed. In addition, no interest in the liquidation account would ever be increased despite any subsequent increase in the related deposit account.

Use of Estimates

Use of estimates

In preparing consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the consolidated balance sheet and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The allowance for credit losses is a material estimate that is particularly susceptible to significant change in the near term.

Fair Value Hierarchy

Fair value hierarchy

The Company groups its assets and liabilities measured at fair value in three levels, based on the markets in which the assets are traded and the reliability of the assumptions used to determine fair value.

Level 1 – Valuation is based on quoted prices in active markets for identical assets. Valuations are obtained from readily available pricing sources for market transactions involving identical assets.

Level 2 – Valuation is based on observable inputs other than Level 1 prices, such as quoted prices for similar assets; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets.

Level 3 – Valuation is based on unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets. Level 3 assets include financial instruments whose value is determined using unobservable inputs to pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation.

Defined benefit pension plan investments in hedge funds are measured using the net asset value per share (or its equivalent) as a practical expedient and have not been classified in the fair value hierarchy.

Accrued Interest Receivable

The Company elected not to measure an allowance for credit losses for accrued interest receivable and instead elected to reverse interest income on loans or securities that are placed on nonaccrual status, which is generally when the instrument is 90 days past due, or earlier if the Company believes the collection of interest is doubtful. The Company has concluded that this policy results in the timely reversal of uncollectible interest.

Allowance for Credit Losses-Loans

The allowance for credit losses is evaluated on a regular basis by management. This evaluation is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available.

For the year ended June 30, 2025, the Company measured the allowance for credit losses using the Scaled CECL Allowance for Losses Estimator (“SCALE”) which has asset size limitations for institutions to use the methodology. Effective July 1, 2025 the Company could not longer use SCALE and changed its Allowance for Credit Loss methodology to use a quantitative Discounted Cash Flow (“DCF”) model combined with the assessment of certain qualitative factors.

Collectively evaluated loans

The allowance for credit losses is established based upon the Company's current estimate of expected lifetime credit losses on loans measured at amortized cost. Credit losses are charged against the allowance when management's assessments confirm that the Company will not collect the full amortized cost basis of a loan. Subsequent recoveries, if any, are credited to the allowance. The Company estimates credit losses for financial assets on a collective basis for loans sharing similar risk characteristics. The Company segments financial assets with similar risk characteristics and has elected to segment its loans based on Federal Call codes used for reporting loans to the Federal Deposit Insurance Corporation as part of the Call Report process. These segments are collectively evaluated for expected credit losses using a quantitative DCF model combined with an assessment of certain qualitative factors designed to address forecast risk and model risk inherent in the quantitative model output. The Company has elected to use this approach because DCF models allow for effective incorporation of a reasonable and supportable forecast in a directionally consistent and objective manner and peer data is available for certain inputs such as the probability of default and the loss given default. The quantitative model utilizes a loss factor based approach to

estimate expected credit losses, which are derived from industry peer loss experience. The model estimates expected credit losses using loan level data over the estimated life of the exposure, considering the effect of prepayments. Economic forecasts are incorporated into the estimate over a reasonable and supportable forecast period, beyond which is a reversion to the historical long-run average using the straight-line reversion method. Management periodically evaluates a reasonable and supportable forecast period and a reversion period to be appropriate for purposes of estimating expected credit losses. The qualitative risk factors impacting the expected risk of loss within the portfolio include the following:

•

changes in the Company’s loan policies, procedures and strategies;

•

changes in international, national, regional, and local economic and business conditions;

•

changes in the nature and volume of the portfolio and terms of loans;

•

changes in experience, depth, and ability of lending management;

•

changes in the volume, trend, and severity of past due financial assets;

•

changes in the quality of the organization’s loan review system;

•

changes in the value of underlying collateral for collateral-dependent loans;

•

the existence and effect of any concentrations of credit, and changes in the level of such concentrations; and

•

the effect of competition and legal/regulatory requirements on the portfolio.

Individually Evaluated Loans

Loans that do not share similar risk characteristics with any pools of assets are subject to individual evaluation and are removed from the collectively assessed pools to avoid double counting. This includes loans on non-accrual and loans that are 90 days or greater past due. For the loans that will be individually evaluated, the Company will use either a discounted cash flow ("DCF") approach or a fair value of collateral approach. The latter approach will be used for loans that are collateral dependent, that is, when the borrower is experiencing financial difficulty and repayment is expected to be provided substantially through the operation or sale of the collateral, expected credit losses are based on fair value of the collateral at the reporting date, adjusted for selling costs as appropriate.

Unallocated component

An unallocated component may be maintained to cover uncertainties that could affect management’s estimate of probable losses. The unallocated portion of the allowance reflects the margin of imprecision inherent in the underlying assumptions used in the methodologies for estimating collectively and individually evaluated loans in the portfolio.

Allowance for Credit Losses- Off-Balance Sheet Credit Exposures

The Company has off-balance sheet financial instruments, which include commitments to extend credit, standby letters of credit and commercial letters of credit. The Company estimates expected credit losses over the contractual period in which the Company is exposed to risk via a contractual obligation to extend credit, unless that obligation is unconditionally cancellable by the Company.

The Company’s allowance for credit losses on off-balance sheet credit exposures is recognized as a liability in accrued expenses and other liabilities on the consolidated balance sheets, with adjustments to the reserve recognized in the provision for credit losses in the consolidated statements of operations. The credit risk associated with these commitments is evaluated in a manner similar to the allowance for credit losses on loans with an additional assumption of probability of funding.

Derivatives and Hedging

The Company follows Accounting Standards Codification (“ASC”) Topic 815, Derivatives and Hedging, with regard to disclosure requirements for derivatives and hedging activities, with the intent to provide users of financial statements with an enhanced understanding of: (a) how and why an entity uses derivative instruments, (b) how the entity accounts for derivative instruments and related hedged items, and (c) how derivative instruments and related hedged items affect an entity’s financial position and performance. Qualitative disclosures explain the Company’s objectives and strategies for using derivatives, and quantitative disclosures are made regarding the fair value of, and gains and losses on, derivative instruments, and about credit-risk-related contingent features in derivative instruments.

As required by ASC 815, the Company reports all derivatives on its balance sheet at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting, and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting.

Derivatives designated and qualifying as a hedge of the exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. Derivatives designated and qualifying as a hedge of the exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. In a fair value hedge, hedge accounting generally provides for the matching of the timing of gain or loss recognition on the hedging instrument with the recognition of the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk.

Recent Accounting Pronouncements

Recent accounting pronouncements

Management has not identified any Accounting Standards Updates that have been issued but are not yet effective and could have a significant impact on the Company’s financial reporting or disclosure requirements.