Significant Accounting Policies 10k(Policies)

The accounting and financial reporting policies of Columbia Banking System, Inc. conform to accounting principles generally accepted in the United States of America and with prevailing practices within the banking and securities industries. All references in this report to "Columbia," "we," "our," or "us" or similar references mean the Company and its subsidiaries, including the wholly-owned banking subsidiary Columbia Bank (the "Bank"). FinPac is a commercial equipment leasing company and a wholly-owned subsidiary of the Bank. The accompanying interim consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, and the Bank's wholly-owned subsidiaries. All inter-company balances and transactions have been eliminated. The consolidated financial statements have not been audited. A more detailed description of the Company's accounting and financial reporting policies is included in the Company's Annual Report on Form 10-K for the year ended December 31, 2025. These interim consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes contained in the Company's Annual Report on Form 10-K for the year ended December 31, 2025.

Basis of Presentation - In preparing these consolidated financial statements, the Company has evaluated events and transactions subsequent to March 31, 2026, for potential recognition or disclosure. In management's opinion, all accounting adjustments necessary to accurately reflect the financial position and results of operations on the accompanying financial statements have been made. These adjustments include those that are normal and recurring in nature and considered necessary for a fair presentation. The results for interim periods are not necessarily indicative of results for the full year or any other interim period.

In 2025, management elected to change the presentation of the Company's financial statements and accompanying footnote disclosures from thousands to millions. The change in presentation had no material impact on previously reported financial information, but certain amounts reported for prior periods may differ by insignificant amounts due to the nature of rounding relative to the change in presentation. In addition, historical percentages and per share amounts presented may not add to their respective totals or recalculate due to rounding.

Application of New Accounting Guidance

Standard

Description

Effective Date

Effect on the Financial Statements or Other Significant Matters

ASU No. 2025-05—Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses for Accounts Receivable and Contract Assets

The amendments provide a practical expedient related to the estimation of expected credit losses for certain current accounts receivable and contract assets arising from transactions accounted for under ASC 606.

Annual and interim periods beginning after December 15, 2025.

The Company adopted the guidance on January 1, 2026, and it did not have a material impact on the Company's consolidated financial statements.

ASU No. 2024-04—Debt—Debt with Conversion and Other Options (Subtopic 470-20): Induced Conversions of Convertible Debt Instruments

The amendment clarifies the accounting for induced conversions of convertible debt instruments and associated disclosure requirements.

Annual and interim periods beginning after December 15, 2025.

The Company adopted the guidance on January 1, 2026, and it did not have a material impact on the Company's consolidated financial statements.

Significant Accounting Standards Issued but Not Yet Adopted

Standard

Description

Effective Date

Effect on the Financial Statements or Other Significant Matters

ASU Update 2025-11

Interim Reporting (Topic 270): Narrow-Scope Improvements

The amendments clarify interim reporting disclosure requirements, consolidates guidance into Topic 270, and establishes a principle for disclosing material events occurring since the prior annual reporting period.

Fiscal years beginning after December 15, 2027, including interim periods within those annual reporting periods. Early adoption is permitted.

The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements.

ASU Update 2025-09

Derivatives and Hedging (Topic 815): Hedge Accounting Improvements

The amendments improve hedge accounting under ASC 815 by expanding and simplifying hedge accounting by increasing eligibility for certain hedging strategies and instruments and improving alignment with entities’ risk management activities.

Fiscal years beginning after December 15, 2026, including interim periods within those annual reporting periods. Early adoption is permitted.

The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements.

ASU No. 2025-08

Financial Instruments—Credit Losses (Topic 326): Purchased Loans

The amendments update the accounting for purchased loans under ASC 326 by eliminating the distinction between purchased credit-deteriorated (PCD) and non-PCD loans and require recognition of an allowance for credit losses at acquisition under a single accounting model.

Fiscal years beginning after December 15, 2026, including interim periods within those annual reporting periods. Early adoption is permitted.

The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements.

ASU No. 2025-06 Intangibles — Goodwill

and Other — Internal-Use Software

(Subtopic 350-40): Targeted

Improvements to the Accounting for

Internal-Use Software

The amendments modernize the accounting for internal-use software by revising capitalization criteria, eliminating project stage guidance, and consolidating website development guidance into Topic 350‑40.

Fiscal years beginning after December 15, 2027, including interim periods within those annual reporting periods. Early adoption is permitted.

The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements.

ASU No. 2024-03 Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses

These amendments require enhanced disclosures disaggregating significant income statement expense categories.

Fiscal years beginning after December 15, 2026, and for interim periods beginning after December 15, 2027. Early adoption is permitted.

The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements.