X0508 4 2024-05-10 0000354190 Arthur J. Gallagher & Co. AJG 0001222374 HOWELL DOUGLAS K 2850 GOLF ROAD ROLLING MEADOWS IL 60008-4002 1 VP & Chief Financial Officer 0 Common Stock 2024-05-10 4 S 0 13992 248.13 D 82959.5662 D Common Stock 2024-05-10 4 S 0 2008 250.36 D 80951.5662 D Common Stock 3165 I By Spouse Common Stock 367.575 I Gallagher 401(k) plan account The price reported is an average weighted price. The shares were sold in multiple transactions on 5/10/2024 at prices ranging from $248.00 to $248.66. The reporting person will provide to the Securities and Exchange Commission staff, the issuer, or any security holder of the issuer, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in the footnotes to this Form 4. The price reported is an average weighted price. The shares were sold in multiple transactions on 5/10/2024 at prices ranging from $250.29 to $250.46. The reporting person has no voting or invesment power over these shares and disclaims beneficial ownership. /s/ Ryan Session, by power of attorney 2024-05-14