Our Series A preferred stock is considered a participating security which requires the use of the two-class method for the computation of basic and diluted per share amounts. Under the two-class method, earnings available to common stockholders for the period are allocated between common stockholders and participating securities according to dividends accumulated and participation rights in undistributed earnings. Net loss attributable to common stockholders is not allocated to the convertible preferred stock as the holder of the Series A preferred stock does not have a contractual obligation to share in losses. Basic net loss attributable to common stockholders per share is computed by dividing net loss available to common stockholders by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss attributable to common stockholders per share is computed by dividing the net loss available to common stockholders for the period by the weighted average number of common and common equivalent shares outstanding during the period. Diluted net loss attributable to common stockholders per share reflects all potential dilutive common stock equivalent shares, including conversion of preferred stock, stock options, restricted stock units and shares to be issued under our employee stock purchase program.


	Three Months Ended March 31,
		2023		2022
Numerator:
Net loss attributable to common stockholders		$	(28,048)	$	(39,960)
Denominator:
Shares used in per share calculation – basic		27,648		27,278
Dilutive effect of common stock		—		—
Shares used in per share calculation — diluted		27,648		27,278
Net loss attributable to common stockholders per share – basic and diluted		$	(1.01)	$	(1.46)

For each of the three months ended March 31, 2023 and 2022, we had securities outstanding that could potentially dilute per share amounts, but the shares from the assumed conversion or exercise of these securities were excluded in the computation of diluted net loss per share as their effect would have been anti-dilutive. The number of outstanding anti-dilutive shares that were excluded from the computation of diluted net loss per share consisted of the following (in thousands):