Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders of Spero Therapeutics, Inc. was calculated as follows (in thousands, except share and per share amounts):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
Numerator:
Net loss	$	(3,205	)	$	(11,675	)	$	(28,385	)	$	(73,186	)
Net loss attributable to common stockholders	$	(3,205	)	$	(11,675	)	$	(28,385	)	$	(73,186	)
Denominator:
Weighted average common shares outstanding, basic and diluted		52,710,280			35,882,076			52,603,709			33,834,198
Net loss per share, basic and diluted	$	(0.06	)	$	(0.33	)	$	(0.54	)	$	(2.16	)

Summary of Shares Excluded From the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders

The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Options to purchase common stock		2,915,190		4,015,661		2,915,190		4,015,661
Unvested RSUs and PSUs		4,832,644		1,145,760		4,832,644		1,145,760
		7,747,834		5,161,421		7,747,834		5,161,421