Provisions in the federal income tax code that treat married couples as one tax unit and cohabiting couples as two tax units result in both marriage penalties and bonuses. This analysis uses data from the 2002 National Survey of America's Families (NSAF) to show the extent to which low-income, cohabiting parents face marriage penalties and bonuses under 2003 tax law and 2008 tax law, when current marriage related provisions from the Economic Growth and Tax Relief Reconciliation Act of 2001 (EGTRRA) phase-in completely.