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Net Loss per Share (Tables)
9 Months Ended
Sep. 30, 2019
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,

 

 

 

2019

 

 

2018

 

 

2019

 

 

2018

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Numerator:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Net loss

 

$

(17,717

)

 

$

(10,463

)

 

$

(35,939

)

 

$

(31,063

)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Denominator:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weighted average common shares outstanding,

   basic and diluted

 

 

18,659,079

 

 

 

17,471,462

 

 

 

17,859,829

 

 

 

15,417,087

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Net loss per share, basic and diluted

 

$

(0.95

)

 

$

(0.60

)

 

$

(2.01

)

 

$

(2.01

)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary of Shares Excluded From the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders The Company excluded the following potential common shares, 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,

 

 

 

2019

 

 

2018

 

 

2019

 

 

2018

 

Options to purchase common stock

 

 

3,094,930

 

 

 

2,186,378

 

 

 

3,094,930

 

 

 

2,186,378

 

Unvested restricted stock units

 

 

50,000

 

 

 

 

 

 

50,000

 

 

 

 

Series A convertible preferred stock (as converted to common shares)

 

 

1,720,000

 

 

 

2,220,000

 

 

 

1,720,000

 

 

 

2,220,000

 

Series B convertible preferred stock (as converted to common shares)

 

 

1,000,000

 

 

 

 

 

 

1,000,000

 

 

 

 

 

 

 

5,864,930

 

 

 

4,406,378

 

 

 

5,864,930

 

 

 

4,406,378