X0306 4 2021-12-02 0000875045 BIOGEN INC. BIIB 0001875506 Izzar Rachid 225 BINNEY STREET CAMBRIDGE MA 02142 1 Head of Alzheimer's Disease Common Stock 2021-12-02 4 M 0 372 228.52 A 1271 D Common Stock 2021-12-02 4 F 0 165 228.52 D 1106 D Restricted Stock Unit 0 2021-12-02 4 M 0 372 0 D 2022-12-02 Common Stock 372 1342 D Restricted Stock Unit 0 2021-12-02 4 J 0 484 0 D 2022-12-02 Common Stock 484 858 D This award was granted to the reporting person on December 2, 2019. The number of RSUs reported represents the maximum possible number of shares that are eligible for vesting, which is 200% of the number of shares at target payout. One-third of these RSUs are eligible to vest on each of the first three anniversaries of the grant date. The actual number of shares that will vest on each vesting date will be determined by comparing the price of Biogen common stock on such vesting date to the price on the grant date (i.e., number of vested shares = number of shares at target payout times [the 30-day average closing stock price ending on the vesting date divided by the 30-day average closing stock price following and including the grant date]). This number represents the difference between the maximum possible number of shares that were eligible for vesting and the actual number that vested. /s/ Wendell Taylor, attorney-in-fact for Rachid Izzar 2021-12-06