Basic net income (loss) per share is calculated by dividing the net loss attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of common shares outstanding during the period.

Diluted net income (loss) per share is computed by dividing the net income (loss) attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of dilutive common shares outstanding during the period. Dilutive shares outstanding is calculated by adding to the weighted shares outstanding any potential (unissued) shares of common stock from outstanding stock options based on the treasury stock method. Outstanding stock options were not included in the diluted net income (loss) per share calculation because in a period when a net loss from continuing operations is reported, all common stock equivalents are excluded from the calculation because they would have an anti-dilutive effect, meaning the income (loss) per share would be reduced. Therefore, in periods where a net loss from continuing operations is reported, there is no difference in basic and dilutive income (loss) per share.

Stock options are excluded from the calculation of diluted income (loss) per share because the net income (loss) for the three months ended March 31, 2024 and 2023 causes such securities to be anti-dilutive. Outstanding options excluded from the calculation of diluted income (loss) per share for the three months ended March 31, 2024 and 2023 are shown in the chart below:


	Three Months Ended March 31,
(in thousands)	2024		2023
Outstanding options to purchase common stock		344		695