Results of Operations · Reg FD Disclosure

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 __________________________ Form 8-K __________________________ CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 April 30, 2026 Date of Report: (Date of earliest event reported) __________________________ ARTHUR J. GALLAGHER & CO. (Exact name of registrant as specified in its charter) __________________________ Delaware 1-09761 36-2151613 (State or other jurisdiction of incorporation or organization) (Commission File Number) (I.R.S. Employer Identification Number) 2850 Golf Road , Rolling Meadows , Illinois 60008 , ( 630 ) 773-3800 (Address, including zip code and telephone number, including area code, of registrant’s principal executive offices) Not Applicable (Former name or former address, if changed since last report) __________________________ Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) Securities registered pursuant to Section 12(b) of the Act: Title of each class Trading Symbol(s) Name of each exchange on which registered Common Stock, $1.00 par value AJG New York Stock Exchange Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐ Item 2.02.   Results of Operations and Financial Condition On April 30, 2026, Arthur J. Gallagher & Co. (the Company) issued a press release setting forth the Company’s financial results for the quarter ended March 31, 2026 (the Earnings Release). A copy of the Earnings Release is attached hereto as Exhibit 99.1. Item 7.01.   Regulation FD Disclosure In connection with the filing of the Earnings Release, the Company made materials entitled “Supplemental Quarterly Data” and “CFO Commentary” available through the investor relations page of its website. The CFO Commentary includes certain estimates relating to 2026 and other future results. Item 9.01.   Financial Statements and Exhibits 99.1 Press release, dated April 30, 2026, issued by Arthur J. Gallagher & Co. 104 The cover page from this Current Report on Form 8-K, formatted in Inline XBRL. SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. ARTHUR J. GALLAGHER & CO. Date: April 30, 2026 By: /s/ Douglas K. Howell Douglas K. Howell Vice President and Chief Financial Officer