-9. Net loss per share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2019		2018		2019		2018
Numerator:
Net loss	$	(15,554)	$	(11,148)	$	(28,144)	$	(20,242)
Accretion of redeemable convertible preferred stock to redemption value		—		(251)		—		(321)
Net loss attributable to common stockholders, basic and diluted	$	(15,554)	$	(11,399)	$	(28,144)	$	(20,563)
Denominator:
Weighted average common shares outstanding, basic and diluted		28,024,779		127,141		10,589,119		86,884
Net loss per share attributable to common stockholders, basic and diluted	$	(0.56)	$	(89.66)	$	(2.66)	$	(236.67)

The Company excluded 42,667 shares and 99,259 shares of restricted common stock, presented on a weighted average basis, from the calculations of basic net loss per share attributable to common stockholders for the three months ended September 30, 2019 and 2018, respectively, because those shares had not vested. The Company excluded 56,679 shares and 139,516 shares of restricted common stock, presented on a weighted average basis, from the calculations of basic net loss per share attributable to common stockholders for the nine months ended September 30, 2019 and 2018, respectively, because those shares had not vested.

The Company’s potentially dilutive securities, which include stock options, unvested restricted common stock and redeemable convertible preferred stock, have been excluded from the computation of diluted net loss per share attributable to common stockholders as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. 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 and nine months ended
	September 30,
	2019	2018
Options to purchase common stock	2,417,234	740,767
Shares to be purchased under employee stock purchase plan	2,626	—
Unvested restricted stock	421,066	94,338
Redeemable convertible preferred stock (as converted to common stock)	—	7,368,894
Total	2,840,926	8,203,999