The Internal Revenue Service has announced that same sex couples legally married in a state whose laws authorize such a marriage will be deemed to be married for Federal tax purposes, even if they live in a state (such as Florida) that does not recognize such marriage.  In other words, the validity of a same sex marriage for Federal tax purposes will be determined by the law of the state in which the marriage was entered into, not the law of the state where the couple lives.  However, a domestic partnership, civil union, or similar formal relationship will not be treated as a marriage.

As a result of this ruling, validly married same sex couples will have the benefits, responsibilities, and protections provided for opposite sex married couples under Federal tax law. 

This announcement has an effective date of September 16, 2013, meaning that same sex married couples must report as married for Federal tax purposes beginning on that date.  Affected couples may also rely on this ruling for prior original and amended returns and claims for credit or refund if the time frame for such return or claim is otherwise still open for tax purposes.

Affected same sex couples will need to determine filing obligations as well as opportunities for benefiting from amending prior year returns.  All types of Federal tax laws should be considered, including without limitation income tax, gift tax, and estate tax.  For example, same sex couples may now provide for their spouses in their estate planning documents with full access to marital deduction planning.