Earnings per Share (Tables)

3 Months Ended

Mar. 31, 2025

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 Three Months Ended March 31,
(In millions)	2025		2024
Numerator:
Net income attributable to Biogen Inc.	$	240.5	$	393.4
Denominator:
Weighted average number of common shares outstanding	146.1		145.2
Effect of dilutive securities:
Time-vested restricted stock units	0.5		0.5
Performance stock units settled in stock	—		0.2
Dilutive potential common shares	0.5		0.7
Shares used in calculating diluted earnings per share	146.6		145.9