Net Loss Per Common Share (Tables)

9 Months Ended

Sep. 30, 2012

Net Loss Per Common Share

Schedule of computation of basic and diluted net loss per share available to common stockholders

	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	)

Schedule of potentially dilutive securities excluded from computation of diluted weighted average shares

	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