Net Loss Per Common Share

9 Months Ended

Sep. 30, 2012

Net Loss Per Common Share

Net Loss Per Common Share

4.  Net Loss Per Common Share

Basic net loss per share is calculated by dividing the net loss attributable 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 attributable 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 for the three and nine months ended September 30, 2011 and 2012:

	Three months ended September 30,						Nine months endedSeptember 30,
(in thousands, except per share amount)	2011			2012			2011			2012
Net Loss Per Share:
Numerator:
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$	(18,599	)	$	(23,199	)	$	(61,107	)	$	(66,509	)
Plus: Unaccreted dividends on convertible preferred stock	(2,062		)	—			(5,728		)	(2,107		)
Net loss available to common stockholders—basic and diluted	(20,661		)	(23,199		)	(66,835		)	(68,616		)
Denominator:
Weighted-average common shares—basic and diluted	11,389			93,724			11,292			65,487
Net loss per share available to common stockholders—basic and diluted	$	(1.81	)	$	(0.25	)	$	(5.92	)	$	(1.05	)

The following common stock equivalents of potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as of September 30, 2011 and 2012, as the Company recorded a net loss in all periods and, therefore, they would be anti-dilutive:

	As of September 30,
(in thousands)	2011	2012
Convertible preferred stock	66,256	—
Options to purchase common stock	17,522	19,812
Convertible preferred stock warrants	303	—
Common stock warrants	2,937	2,891