Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2024

Earnings Per Share [Abstract]

Basic and diluted earnings per share

Basic and diluted shares outstanding used in our earnings per share calculation are calculated as follows:

	For the Years Ended December 31,
(In millions)	2024		2023		2022
Numerator:
Net income attributable to Biogen Inc.	$	1,632.2	$	1,161.1	$	3,046.9
Denominator:
Weighted-average number of common shares outstanding	145.6		144.7		145.3
Effect of dilutive securities:
Time-vested restricted stock units	0.3		0.7		0.5
Market stock units	—		—		0.1
Performance stock units settled in stock	—		0.2		0.1
Dilutive potential common shares	0.3		0.9		0.7
Shares used in calculating diluted earnings per share	145.9		145.6		146.0