In this paper we estimate the impacts on income tax collections of legalizing same‐sex marriage. We utilize new individual‐level data sources to estimate the federal income tax consequences of legalizing same‐sex marriages. These data sources also allow us to estimate the impact of legalization on state income tax collections. We find that 23 states would realize a net fiscal benefit from legalization, while 21 states would experience a decline in revenue. The potential (annual) changes in state tax revenue range from negative $29 million in California to positive $16 million in New York. At the federal level, our estimates suggest an overall reduction in revenues, ranging from a potential loss of $187 million to $580 million. Overall, we find that the federal and state impacts are quite modest. We also find that our estimates are only marginally affected by alternative assumptions about how many same‐sex couples will choose to marry and which partner will claim any children for tax deduction purposes.