X0508 4 2024-05-02 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 2024-05-02 4 M 0 4687.984 0 A 98918.5502 D Common Stock 2024-05-02 4 F 0 1966.984 238.54 D 96951.5662 D Common Stock 3165 I By Spouse Common Stock 367.575 I Gallagher 401(k) plan account Phantom Stock 2024-05-02 4 M 0 4687.984 0 D Common Stock 4687.984 2467.86 D The reporting person has no voting or invesment power over these shares and disclaims beneficial ownership. Each share of phantom stock represents a right to receive one share of Gallagher common stock. These shares represent awards under the Age 62 Plan, a nonqualified deferred compensation plan of the Company, which have been deemed invested in Company common stock at the election of the reporting person. Participants vest in these awards when they attain age 62, or after a one-year period for participants who have attained age 61. This filing reports the distribution of shares, and the withholding of shares for taxes, in connection with an Age 62 Plan award that vested earlier in the year during a quarterly trading blackout period. /s/ Ryan Session, by power of attorney 2024-05-06