Exhibit 99.3

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UNAUDITED PRO FORMA CONDENSED COMBINED CONSOLIDATED FINANCIAL STATEMENTS

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The following unaudited pro forma condensed combined consolidated financial information and notes thereto have been prepared to give effect to the merger and related transaction accounting adjustments (“pro forma adjustments”) described in the accompanying notes.

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On July 14, 2026, Catalyst Bancorp, Inc. and Catalyst Bank (collectively referred to as “Catalyst”) completed the acquisitions of Lakeside Bancshares, Inc. and Lakeside Bank (collectively referred to as “Lakeside”) pursuant to an Agreement and Plan of Share Exchange and Merger dated April 7, 2026 (the “Merger Agreement”) by and among Catalyst and Lakeside. The Merger Agreement provided for the acquisition of all shares of common stock of Lakeside Bancshares, Inc. by Catalyst Bancorp, Inc. through a share exchange for cash, followed immediately by the merger of Lakeside Bancshares, Inc. with and into Catalyst Bancorp, Inc. and the subsequent merger of Lakeside Bank with and into Catalyst Bank, with Catalyst Bancorp, Inc. and Catalyst Bank continuing as the surviving entities.

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The accompanying unaudited pro forma condensed combined consolidated balance sheet as of March 31, 2026 combines the historical consolidated balance sheets of Catalyst and Lakeside, giving effect to the merger as if it had been completed on March 31, 2026. The accompanying unaudited pro forma condensed combined consolidated income statements for the three months ended March 31, 2026 and the year ended December 31, 2025 combine the historical consolidated income statements of Catalyst and Lakeside, giving effect to the merger as if it had been completed on January 1, 2025.

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The historical consolidated financial statements of Catalyst and Lakeside have been adjusted in the accompanying unaudited pro forma condensed combined consolidated financial information to give effect to the pro forma events that are necessary to account for the merger in accordance with accounting principles generally accepted in the United States of America. The unaudited pro forma adjustments are based on information and certain assumptions that Catalyst believes are reasonable. The following unaudited pro forma condensed combined consolidated financial information does not reflect the costs of any integration activities or benefits that may result from the realization of future cost savings from operating efficiencies. Certain reclassifications have also been made to align Lakeside’s historical financial statement presentation to Catalyst’s.

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The following unaudited pro forma condensed combined consolidated financial information and related accompanying notes should be read in conjunction with (i) the separate historical audited consolidated financial statements of Catalyst as of and for the year ended December 31, 2025, and the related notes, included in Catalyst’s Annual Report on Form 10-K for the period ended December 31, 2025, filed with the U.S. Securities and Exchange Commission (“SEC”) on March 31, 2026, (ii) the separate historical unaudited consolidated financial statements of Catalyst as of and for the three months ended March 31, 2026, and the related notes, included in Catalyst’s Form 10-Q for the period ended March 31, 2026, filed with the SEC on May 15, 2026, (iii) the separate historical audited consolidated financial statements of Lakeside as of and for the year ended December 31, 2025, and the related notes, included as Exhibit 99.1, and (iv) the separate historical unaudited consolidated financial statements of Lakeside as of and for the three months ended March 31, 2026, and the related notes, included as Exhibit 99.2.

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The unaudited pro forma condensed combined consolidated financial information is provided for illustrative information purposes only. The unaudited pro forma condensed combined consolidated financial information is not necessarily, and should not be assumed to be, an indication of the actual results that would have been achieved had the merger been completed as of the dates indicated or that may be achieved in the future.

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The merger is being accounted for as a business combination using the acquisition method, with Catalyst as the accounting acquirer in accordance with Accounting Standards Codification (“ASC”) Topic 805, Business Combinations (“ASC 805”). Under this method of accounting, the aggregate purchase consideration will be allocated to Lakeside’s assets acquired and liabilities assumed based upon their estimated fair values at the date of acquisition. The process of valuing Lakeside’s net assets immediately prior to the merger and evaluating accounting policies for conformity is preliminary. Any differences between the estimated fair value of the purchase consideration and the estimated fair value of the assets acquired and liabilities assumed will be recorded as goodwill.

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The unaudited pro forma condensed combined consolidated financial information also does not consider any potential effects of changes in market conditions on revenues, expense efficiencies, severance and retention expenses, asset dispositions, and share repurchases, among other factors. In addition, the preliminary allocation of the pro forma purchase price reflected in the unaudited pro forma condensed combined consolidated financial information is subject to adjustment and may vary significantly from the actual purchase price allocation that will be recorded upon finalization of estimated fair values of the assets and liabilities acquired.

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As of the date of this unaudited pro forma condensed combined consolidated financial information, Catalyst is in the process of completing its initial valuation analysis and calculations necessary to arrive at the required estimates of the fair values of the Lakeside assets acquired and liabilities assumed. Accordingly, the fair value estimates assigned to certain assets and liabilities of Lakeside are preliminary. Final adjustments may differ from the amounts reflected in the unaudited pro forma condensed combined consolidated financial information, and the differences may be material.

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Further, Catalyst is in the process of identifying any adjustments necessary to conform Lakeside’s accounting policies to those of Catalyst. As more information becomes available, Catalyst will perform a more detailed review of Lakeside’s accounting policies. As a result of that review, differences could be identified between the accounting policies of the two companies that, when conformed, could have a material impact on the combined company’s financial information.

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As a result of the foregoing, the pro forma adjustments are preliminary and are subject to change as additional information becomes available and as additional analysis is performed. The preliminary pro forma adjustments have been made solely for the purpose of providing the unaudited pro forma condensed combined consolidated financial information.

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Fair value estimates related to the assets and liabilities from Lakeside are subject to adjustment for up to one year after the closing date of the acquisition as additional information becomes available. Any changes in the fair values of the net assets acquired or total purchase consideration compared with the information shown in the unaudited pro forma condensed combined consolidated financial information may change the amount of the total purchase consideration allocated to goodwill and other assets and liabilities and may impact the combined company’s statement of income. The final purchase consideration allocation may be materially different than the preliminary purchase consideration allocation presented in the unaudited pro forma condensed combined consolidated financial information.

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UNAUDITED PRO FORMA CONDENSED COMBINED CONSOLIDATED BALANCE SHEET

AS OF MARCH 31, 2026

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The accompanying Notes are an integral part of these condensed combined consolidated financial statements.

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UNAUDITED PRO FORMA CONDENSED COMBINED CONSOLIDATED STATEMENT OF INCOME

FOR THE THREE MONTHS ENDED MARCH 31, 2026

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The accompanying Notes are an integral part of these condensed combined consolidated financial statements.

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UNAUDITED PRO FORMA CONDENSED COMBINED CONSOLIDATED STATEMENT OF INCOME

FOR THE YEAR ENDED DECEMBER 31, 2025

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CATALYST BANCORP, INC.

NOTES TO THE UNAUDITED PRO FORMA CONDENSED COMBINED CONSOLIDATED FINANCIAL STATEMENTS

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NOTE 1. BASIS OF PRESENTATION

On July 14, 2026, Catalyst completed the acquisition of Lakeside pursuant to the Merger Agreement by and among Catalyst and Lakeside. Effective July 14, 2026, Catalyst acquired 100% of the outstanding shares of Lakeside in exchange for $19.58 per share in cash, or $41.1 million in aggregate.

The accompanying unaudited pro forma condensed consolidated combined balance sheet as of March 31, 2026 combines the historical consolidated balance sheets of Catalyst and Lakeside, giving effect to the merger as if it had been completed on March 31, 2026. The accompanying unaudited pro forma condensed combined income statements for the three months ended March 31, 2026 and the year ended December 31, 2025 combine the historical consolidated income statements of Catalyst and Lakeside, giving effect to the merger as if it had been completed on January 1, 2025.

The merger is being accounted for as a business combination using the acquisition method, with Catalyst as the accounting acquirer in accordance with ASC 805. Under the acquisition method of accounting, the purchase consideration is allocated to the identifiable assets acquired and liabilities assumed based on their estimated fair values as of the acquisition date. Any excess of the purchase consideration over the estimated fair value of the identifiable net assets acquired is recognized as goodwill.

The pro forma financial information includes estimated adjustments to record the assets and liabilities of Lakeside at their respective fair values and represents management’s estimates based on available information. The pro forma adjustments included herein may be revised as additional information becomes available and as additional analysis is performed. The final allocation of the purchase price will be determined after completion of a final analysis to determine the fair values of Lakeside’s tangible and identifiable intangible assets and liabilities as of the acquisition date and any differences could be material.

The unaudited pro forma condensed combined consolidated financial information does not reflect any anticipated synergies, operating efficiencies, or cost savings that may result from the merger, nor any acquisition and integration costs that may be incurred. The pro forma adjustments represent management’s best estimates and are based upon currently available information and certain assumptions that management believes are reasonable under the circumstances.

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NOTE 2. PRO FORMA ADJUSTMENTS

The following pro forma adjustments have been reflected in the unaudited pro forma condensed combined consolidated financial information. All adjustments are based on current valuations, estimates and assumptions that are subject to change and such change could be material.

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The pre-tax, pro forma estimated accretion and amortization for certain estimated pro forma fair value discounts and premiums are presented in the table below. The amounts for 2026 reflect the nine month period ending December 31, 2026 and the remaining periods are for the twelve months ending December 31.

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NOTE 3. PRO FORMA ALLOCATION OF PURCHASE PRICE

The following shows the pro forma allocation of the consideration paid for Lakeside’s common equity to the acquired identifiable assets and liabilities assumed and the pro forma goodwill generated from the transaction.

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