In the wake of United States v. Windsor, the IRS determined that a validly married same-sex couple is married for federal tax purposes regardless of their state of residence. A same-sex spouse residing in a state that does not recognize same-sex marriage is required to file federal taxes as married under federal law but is prohibited from filing as married in-state, thereby creating incompatibility—a filing status mismatch—between her federal and state income taxes. In order to resolve this, states should not require a same-sex spouse to prepare a pro forma “unmarried” federal return for state filing purposes, as this is inefficient to administer and enforce, and creates an inequitable compliance burden on the taxpayer. Nor should states delink their base from federal income or remove from their state tax codes all references to federal tax law, as this reduces tax efficiency. Instead, states should place traditional concerns of tax efficiency and equality above narrower same-sex marriage policy objectives when crafting their tax systems. Tax efficiency and equity require that states at least permit resident same-sex married taxpayers to allocate income and deduction figures already computed for their federal returns when preparing their state returns.