Earnings per Share (Tables)

9 Months Ended

Sep. 30, 2023

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 September 30,				For the Nine Months Ended September 30,
(In millions)	2023		2022		2023		2022
Numerator:
Net income (loss) attributable to Biogen Inc.	$	(68.1)	$	1,134.7	$	911.4	$	2,496.5
Denominator:
Weighted average number of common shares outstanding	144.8		144.4		144.7		145.8
Effect of dilutive securities:
Time-vested restricted stock units	—		0.3		0.7		0.3
Performance stock units settled in stock	—		0.1		0.1		0.1
Dilutive potential common shares	—		0.4		0.8		0.4
Shares used in calculating diluted earnings per share	144.8		144.8		145.5		146.2