Net Loss Per Common Share

6 Months Ended

Jun. 30, 2013

Net Loss Per Common Share

Net Loss Per Common Share

3. 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 for the three and six months ended June 30, 2012 and 2013:

	Three months ended June 30,						Six months ended June 30,
(in thousands, except per share amount)	2012			2013			2012			2013
Net Loss Per Share:
Numerator:
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$	(20,026	)	$	(30,082	)	$	(43,310	)	$	(58,235	)
Plus: Unaccreted dividends on convertible preferred stock	(67		)	—			(2,107		)	—
Net loss available to common stockholders—basic and diluted	(20,093		)	(30,082		)	(45,417		)	(58,235		)
Denominator:
Weighted-average common shares—basic and diluted	90,581			96,170			51,214			96,025
Net loss per share available to common stockholders—basic and diluted	$	(0.22	)	$	(0.31	)	$	(0.89	)	$	(0.61	)

The following common stock equivalents of potentially dilutive securities have been excluded from the computation of diluted weighted average shares outstanding as of June 30, 2012 and 2013, as the Company recorded a net loss in all periods and, therefore, they would be anti-dilutive:

	As of June 30,
(in thousands)	2012	2013
Options to purchase common stock	17,455	20,447
Common stock warrants	2,905	2,777

Also excluded from the computation of diluted weighted average shares outstanding as of June 30, 2012 as anti-dilutive were 66,256,000 common stock equivalents of convertible preferred stock and 302,000 common stock equivalents of convertible preferred stock warrants that converted to common stock and common warrants, respectively, upon the closing of our initial public offering in April 2012.