Basis of Presentation and Changes in Significant Accounting Policies	6 Months Ended
Jun. 30, 2026
Basis of Presentation and Changes in Significant Accounting Policies
Basis of Presentation and Changes in Significant Accounting Policies	Note 1 – Basis of Presentation and Changes in Significant Accounting Policies The accounting policies followed in the preparation of the interim consolidated financial statements are consistent with those used in the preparation of the annual financial information. The interim consolidated financial statements reflect all normal and recurring adjustments that are necessary, in the opinion of management, for a fair statement of results for the interim period presented. Results for the period ended June 30, 2026, are not necessarily indicative of the results that may be expected for the year ending December 31, 2026. These interim consolidated financial statements and accompanying notes are unaudited and should be read in conjunction with the audited financial statements and notes included in Old Second Bancorp, Inc.’s (the “Company”) annual report on Form 10-K for the year ended December 31, 2025. Unless otherwise indicated, dollar amounts in the tables contained in the notes to the consolidated financial statements are in thousands. Certain items in prior periods have been reclassified to conform to the current presentation. The Company’s consolidated financial statements are prepared in accordance with United States generally accepted accounting principles (“GAAP”) and follow general practices within the banking industry. Application of these principles requires management to make estimates, assumptions, and judgments that affect the amounts reported in the consolidated financial statements and accompanying notes. These estimates, assumptions, and judgments are based on information available as of the date of the consolidated financial statements. Future changes in information may affect these estimates, assumptions, and judgments, which, in turn, may affect amounts reported in the consolidated financial statements. Recent Accounting Pronouncements The following is a summary of recent accounting pronouncements that have impacted or could potentially affect the Company: ASU 2023-06 – On October 9, 2023, the FASB issued ASU 2023-06 “Disclosure Improvements: Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative.” The amendments in the ASU modify the disclosure or presentation requirements of a variety of topics in the codification. Certain of the amendments represent clarifications to, or technical corrections of, the current requirements. Each amendment in the ASU will only become effective if the SEC removes the related disclosure or presentation requirement from its existing regulations by June 30, 2027. The amendments in this ASU are not expected to have a material impact on the financial statements of the Company. ASU 2024-03 – On November 4, 2024, the FASB issued ASU 2024-03 “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses.” This ASU requires public companies to disclose, in the notes to financial statements, specified information about certain costs and expenses at each interim and annual reporting period. Specifically, they will be required to: (1) Disclose the amounts of (a) purchases of inventory; (b) employee compensation; (c) depreciation; (d) intangible asset amortization; and (e) depreciation, depletion, and amortization recognized as part of oil- and gas-producing activities (or other amounts of depletion expense) included in each relevant expense caption. (2) Include certain amounts that are already required to be disclosed under current generally accepted accounting principles (GAAP) in the same disclosure as the other disaggregation requirements. (3) Disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively. (4) Disclose the total amount of selling expenses and, in annual reporting periods, an entity’s definition of selling expenses. ASU 2024-03 is effective for public business entities for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027, and is not expected to have a material impact on the financial statements of the Company. ASU 2025-01 – On January 6, 2025, the FASB issued ASU 2025-01 “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Clarifying the Effective Date.” ASU 2024-03 is effective for public business entities for annual reporting periods beginning after December 15, 2026, and interim reporting periods within annual reporting periods beginning after December 15, 2027, which dates were clarified in ASU 2025-01. This ASU is not expected to have a material impact on the financial statements of the Company. ASU 2025-03 – On May 12, 2025, the FASB issued ASU 2025-03 “Business Combinations (Topic 805) and Consolidation (Topic 810): Determining the Accounting Acquirer in the Acquisition of a Variable Interest Entity.” This ASU revises current guidance for determining the accounting acquirer for a transaction effected primarily by exchanging equity interests in which the legal acquiree is a variable interest entity that meets the definition of a business. The amendments require an entity to consider the same factors that are currently required for determining which entity is the accounting acquirer in other acquisition transactions. This ASU is effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods within those annual reporting periods. Early adoption is permitted in an interim or annual reporting period in which financial statements have not yet been issued (or made available for issuance). If an entity adopts ASU No. 2025-03 in an interim reporting period, it should adopt it as of the beginning of that interim reporting period or the beginning of the annual reporting period that includes that interim reporting period. An entity should apply ASU 2025-03 on a prospective basis to all business combinations that have an acquisition date that occurs on or after the date of initial application of ASU 2025-03. ASU 2025-03 is not expected to have a material impact on the financial statements of the Company. ASU 2025-08 – On November 12, 2025, the FASB issued ASU 2025-08 “'Financial Instruments—Credit Losses (Topic 326): Purchased Loans.” This ASU expands the population of acquired financial assets accounted for using the gross-up approach. Acquired loans (excluding credit cards) are deemed purchased seasoned loans and accounted for using the gross-up approach upon acquisition if criteria established by the new guidance are met. This change aims to enhance comparability, consistency, and better reflect the economics of acquiring financial assets. ASU 2025-08 is effective for interim and annual periods in fiscal years beginning after December 15, 2026, and is applied prospectively. Early adoption is permitted. Old Second has elected not to early adopt ASU 2025-08 at this time. When adopted, the standard will be adopted prospectively; thus, the accounting for previously completed business combinations will not be impacted. However, adopting this accounting standard is anticipated to have a material impact on the accounting for purchased loans on any business combination completed after adoption. ASU 2025-11 – On December 8, 2025, the FASB issued ASU 2025-11 “Interim Reporting (Topic 270): Narrow-Scope Improvements”. This ASU does not change the fundamental nature of interim reporting or expand or reduce current interim disclosure requirements. The amendments in this ASU: i) clarify that the guidance in Topic 270 applies to all entities that provide interim financial statements and notes in accordance with GAAP; ii) create a comprehensive list in FASB ASC Topic 270 of interim disclosures that are required in interim financial statements and notes in accordance with GAAP; iii) incorporate a disclosure principle, which is modeled after previous SEC guidance, that requires entities to disclose events and changes that occur after the end of the most recent fiscal year that have a material impact on the entity; and iv) improve guidance about information included in and the format of interim financial statements. The amendments in this ASU are effective for public business entities for interim periods within annual periods beginning after December 15, 2027. ASU 2025-11 is not expected to have a material impact on the financial statements of the Company. ASU 2025-12 – On December 17, 2025, the FASB issued ASU 2025-12 “Codification Improvements”. The amendments in this ASU update the FASB ASC for a broad range of topics arising from technical corrections, unintended application of the Codification, clarifications, and other minor improvements. The amendments in the ASU, which addresses 33 issues, affect a wide variety of topics in the Codification and apply to all reporting entities within the scope of the affected accounting guidance. The amendments in this ASU are effective for all entities for annual periods beginning after December 15, 2026, and interim periods within those annual periods. Early adoption is permitted in both interim and annual periods in which financial statements have not yet been issued or made available for issuance. ASU 2025-12 is not expected to have a material impact on the financial statements of the Company. Changes in Significant Accounting Policies Significant accounting policies are presented in Note 1 to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025. These policies, along with the disclosures presented in the other financial statement notes and, in this discussion, provide information on how significant assets and liabilities are valued in the consolidated financial statements and how those values are determined. During the second quarter of 2026, the Company had no changes to significant accounting policies or estimates. Subsequent Events Dividends On July 21, 2026, our Board of Directors declared a cash dividend of $0.07 per share of common stock payable on August 10, 2026, to stockholders of record as of July 31, 2026; dividends of $3.6 million will be paid to stockholders on August 10, 2026.

Basis of Presentation and Changes in Significant Accounting Policies

6 Months Ended

Jun. 30, 2026

Basis of Presentation and Changes in Significant Accounting Policies

Basis of Presentation and Changes in Significant Accounting Policies

Note 1 – Basis of Presentation and Changes in Significant Accounting Policies

The accounting policies followed in the preparation of the interim consolidated financial statements are consistent with those used in the preparation of the annual financial information. The interim consolidated financial statements reflect all normal and recurring adjustments that are necessary, in the opinion of management, for a fair statement of results for the interim period presented. Results for the period ended June 30, 2026, are not necessarily indicative of the results that may be expected for the year ending December 31, 2026. These interim consolidated financial statements and accompanying notes are unaudited and should be read in conjunction with the audited financial statements and notes included in Old Second Bancorp, Inc.’s (the “Company”) annual report on Form 10-K for the year ended December 31, 2025. Unless otherwise indicated, dollar amounts in the tables contained in the notes to the consolidated financial statements are in thousands. Certain items in prior periods have been reclassified to conform to the current presentation.

The Company’s consolidated financial statements are prepared in accordance with United States generally accepted accounting principles (“GAAP”) and follow general practices within the banking industry. Application of these principles requires management to make estimates, assumptions, and judgments that affect the amounts reported in the consolidated financial statements and accompanying notes. These estimates, assumptions, and judgments are based on information available as of the date of the consolidated financial statements. Future changes in information may affect these estimates, assumptions, and judgments, which, in turn, may affect amounts reported in the consolidated financial statements.

Recent Accounting Pronouncements

The following is a summary of recent accounting pronouncements that have impacted or could potentially affect the Company:

ASU 2023-06 – On October 9, 2023, the FASB issued ASU 2023-06 “Disclosure Improvements: Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative.” The amendments in the ASU modify the disclosure or presentation requirements of a variety of topics in the codification. Certain of the amendments represent clarifications to, or technical corrections of, the current requirements. Each amendment in the ASU will only become effective if the SEC removes the related disclosure or presentation requirement from its existing regulations by June 30, 2027. The amendments in this ASU are not expected to have a material impact on the financial statements of the Company.

ASU 2024-03 – On November 4, 2024, the FASB issued ASU 2024-03 “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses.” This ASU requires public companies to disclose, in the notes to financial statements, specified information about certain costs and expenses at each interim and annual reporting period. Specifically, they will be required to: (1) Disclose the amounts of (a) purchases of inventory; (b) employee compensation; (c) depreciation; (d) intangible asset amortization; and (e) depreciation, depletion, and amortization recognized as part of oil- and gas-producing activities (or other amounts of depletion expense) included in each relevant expense caption. (2) Include certain amounts that are already required to be disclosed under current generally accepted accounting principles (GAAP) in the same disclosure as the other disaggregation requirements. (3) Disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively. (4) Disclose the total amount of selling expenses and, in annual reporting periods, an entity’s definition of selling expenses. ASU 2024-03 is effective for public business entities for annual reporting periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027, and is not expected to have a material impact on the financial statements of the Company.

ASU 2025-01 – On January 6, 2025, the FASB issued ASU 2025-01 “Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Clarifying the Effective Date.” ASU 2024-03 is effective for public business entities for annual reporting periods beginning after December 15, 2026, and interim reporting periods within annual reporting periods beginning after December 15, 2027, which dates were clarified in ASU 2025-01. This ASU is not expected to have a material impact on the financial statements of the Company.

ASU 2025-03 – On May 12, 2025, the FASB issued ASU 2025-03 “Business Combinations (Topic 805) and Consolidation (Topic 810): Determining the Accounting Acquirer in the Acquisition of a Variable Interest Entity.” This ASU revises current guidance for determining the accounting acquirer for a transaction effected primarily by exchanging equity interests in which the legal acquiree is a variable interest entity that meets the definition of a business. The amendments require an entity to consider the same factors that are currently required for determining which entity is the accounting acquirer in other acquisition transactions. This ASU is effective for annual reporting periods beginning after December 15, 2026, and interim reporting periods within those annual reporting periods. Early adoption is permitted in an interim or annual reporting period in which financial statements have not yet been issued (or made available for issuance). If an entity adopts ASU No. 2025-03 in an interim reporting period, it should adopt it as of the beginning of that interim reporting period or the beginning of the annual reporting period that includes that interim reporting period. An entity should apply ASU 2025-03 on a prospective basis to all business combinations that have an acquisition date that occurs on or after the date of initial application of ASU 2025-03. ASU 2025-03 is not expected to have a material impact on the financial statements of the Company.

ASU 2025-08 – On November 12, 2025, the FASB issued ASU 2025-08 “'Financial Instruments—Credit Losses (Topic 326): Purchased Loans.” This ASU expands the population of acquired financial assets accounted for using the gross-up approach. Acquired loans (excluding credit cards) are deemed purchased seasoned loans and accounted for using the gross-up approach upon acquisition if criteria established by the new guidance are met. This change aims to enhance comparability, consistency, and better reflect the economics of acquiring financial assets. ASU 2025-08 is effective for interim and annual periods in fiscal years beginning after December 15, 2026, and is applied prospectively. Early adoption is permitted.

Old Second has elected not to early adopt ASU 2025-08 at this time. When adopted, the standard will be adopted prospectively; thus, the accounting for previously completed business combinations will not be impacted. However, adopting this accounting standard is anticipated to have a material impact on the accounting for purchased loans on any business combination completed after adoption.

ASU 2025-11 – On December 8, 2025, the FASB issued ASU 2025-11 “Interim Reporting (Topic 270): Narrow-Scope Improvements”. This ASU does not change the fundamental nature of interim reporting or expand or reduce current interim disclosure requirements. The amendments in this ASU: i) clarify that the guidance in Topic 270 applies to all entities that provide interim financial statements and notes in accordance with GAAP; ii) create a comprehensive list in FASB ASC Topic 270 of interim disclosures that are required in interim financial statements and notes in accordance with GAAP; iii) incorporate a disclosure principle, which is modeled after previous SEC guidance, that requires entities to disclose events and changes that occur after the end of the most recent fiscal year that have a material impact on the entity; and iv) improve guidance about information included in and the format of interim financial statements. The amendments in this ASU are effective for public business entities for interim periods within annual periods beginning after December 15, 2027. ASU 2025-11 is not expected to have a material impact on the financial statements of the Company.

ASU 2025-12 – On December 17, 2025, the FASB issued ASU 2025-12 “Codification Improvements”. The amendments in this ASU update the FASB ASC for a broad range of topics arising from technical corrections, unintended application of the Codification, clarifications, and other minor improvements. The amendments in the ASU, which addresses 33 issues, affect a wide variety of topics in the Codification and apply to all reporting entities within the scope of the affected accounting guidance. The amendments in this ASU are effective for all entities for annual periods beginning after December 15, 2026, and interim periods within those annual periods. Early adoption is permitted in both interim and annual periods in which financial statements have not yet been issued or made available for issuance. ASU 2025-12 is not expected to have a material impact on the financial statements of the Company.

Changes in Significant Accounting Policies

Significant accounting policies are presented in Note 1 to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025. These policies, along with the disclosures presented in the other financial statement notes and, in this discussion, provide information on how significant assets and liabilities are valued in the consolidated financial statements and how those values are determined. During the second quarter of 2026, the Company had no changes to significant accounting policies or estimates.

Subsequent Events

Dividends

On July 21, 2026, our Board of Directors declared a cash dividend of $0.07 per share of common stock payable on August 10, 2026, to stockholders of record as of July 31, 2026; dividends of $3.6 million will be paid to stockholders on August 10, 2026.