BARRETT BUSINESS SERVICES INC

Rule 10b5-1 Trading Arrangements

During the quarter ended December 31, 2025, the executive officers of the Company listed below adopted a “Rule 10b5-1 trading arrangement” (as defined in Item 408 of Regulation S-K adopted under the Exchange Act). There were no “non-Rule 10b5-1 trading arrangements” (as defined in Item 408(c))adopted, modified, orterminated by the Company’s directors and executive officers during the quarter ended December 31, 2025. The Rule 10b5-1 trading arrangements listed below were adopted in accordance with the Company’s Insider Trading Policy. Actual sale transactions made pursuant to the Rule 10b5-1 trading arrangements described below will be disclosed publicly in Section 16 filings with the SEC in accordance with applicable securities laws, rules, and regulations.

(1) Mr. Blotz's Rule 10b5-1 Trading Plan (the "Blotz Plan") provides for the potential sale of up to (i)18,257 shares of common stock beginning on July 3, 2026 upon the vesting of restricted stock units ("RSUs") that are expected to vest on July 1, 2026, and (ii)14,354 shares of common stock beginning on March 16, 2026 from performance stock units ("PSUs") that vested on February 23, 2026. Shares in the Blotz Plan underlying RSUs and PSUs may only be sold following satisfaction of the applicable time-based and performance-based vesting requirements. Additionally, shares will only be sold provided that the market price of the Company’s common stock is higher than minimum threshold prices specified in the Blotz Plan. Due to the minimum threshold prices, the time-based and performance-based vesting requirements, and the number of shares to be withheld to satisfy applicable tax obligations, the exact number of shares to be sold pursuant to the Blotz Plan is not yet determinable. For purposes of this disclosure, we have included the maximum number of shares available to be sold without regard to vesting or withholding conditions. The Blotz Plan is intended to satisfy the affirmative defense of Rule 10b5-1(c) under the Exchange Act.

(2) Mr. Potts’s Rule 10b5-1 Trading Plan (the "Potts Plan") provides for the potential sale of up to (i)11,508 shares of common stock beginning on July 3, 2026 upon the vesting of RSUs that are expected to vest on July 1, 2026, and (ii)6,350 shares of common stock beginning on March 16, 2026 from PSUs that vested on February 23, 2026. Shares in the Potts Plan underlying RSUs and PSUs may only be sold following satisfaction of the applicable time-based and performance-based vesting requirements. Additionally, shares will only be sold provided that the market price of the Company’s common stock is higher than minimum threshold prices specified in the Potts Plan. Due to the minimum threshold prices, the time-based and performance-based vesting requirements, and the number of shares to be withheld to satisfy applicable tax obligations, the exact number of shares to be sold pursuant to the Potts Plan is not yet determinable. For purposes of this disclosure, we have included the maximum number of shares available to be sold without regard to vesting or withholding conditions. The Potts Plan is intended to satisfy the affirmative defense of Rule 10b5-1(c) under the Exchange Act.