Earnings per Share (Tables)

3 Months Ended

Mar. 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 Three Months Ended March 31,
(In millions)	2024		2023
Numerator:
Net income attributable to Biogen Inc.	$	393.4	$	387.9
Denominator:
Weighted average number of common shares outstanding	145.2		144.4
Effect of dilutive securities:
Time-vested restricted stock units	0.5		0.6
Market stock units	—		0.1
Performance stock units settled in stock	0.2		0.1
Dilutive potential common shares	0.7		0.8
Shares used in calculating diluted earnings per share	145.9		145.2