Net Loss Per Common Share

12 Months Ended

Dec. 31, 2012

Net Loss Per Common Share

Net Loss Per Common Share

5. Net Loss Per Common Share

        Basic net loss per share is calculated by dividing the net loss available to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss available to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, convertible preferred stock, stock options and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

        The following table presents the computation of basic and diluted net loss per share available to common stockholders:

	Years ended December 31,
(in thousands, except per share amount)	2010			2011			2012
Net Loss Per Share:
Numerator:
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$	(50,104	)	$	(79,223	)	$	(91,277	)
Plus: Unaccreted dividends on convertible preferred stock		(11,185	)		(7,789	)		(2,107	)
Net loss available to common stockholders—basic and diluted		(61,289	)		(87,012	)		(93,384	)
Denominator:
Weighted-average common shares—basic and diluted		10,994			11,343			72,831
Net loss per share available to common stockholders—basic and diluted	$	(5.57	)	$	(7.67	)	$	(1.28	)

        The following common stock equivalents of potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as of December 31, 2010, 2011 and 2012 as the Company recorded a net loss in all periods and, therefore, they would be anti-dilutive:

	Years ended December 31,
(in thousands)	2010		2011		2012
Convertible preferred stock		55,253		66,256		—
Options to purchase common stock		16,214		17,617		18,066
Convertible preferred stock warrants		306		302		—
Common stock warrants		2,937		2,640		2,842