Currently there are 13 states and the District of Columbia as well as 15 other countries that have legalized same-sex marriage. If you and your partner are married in one of these areas you are now able to file a married filing joint (or married filing separate) federal tax return.
In June 2013, the Supreme Court ruled the federal tax aspects of the Defense of Marriage Act invalid. Therefore, the US Department of the Treasury and the Internal Revenue Service have changed the way same-sex couples are treated for federal tax purposes.
Under the new ruling, same-sex couples will be treated as married for all federal tax purposes, including income, gift and estate taxes. The ruling applies to all federal tax provisions where marriage is a factor, including filing status, claiming personal and dependency exemptions, taking the standard deduction, employee benefits, contributing to an IRA and claiming the earned income tax credit or child tax credit.
Any legally married same-sex (which does not include registered domestic partners, civil unions or other similar formal relationships) must file their tax return as married filing joint or married filing separate. This is not impacted by the area in which you currently reside, as long as your place of marriage recognizes your relationship as a legal marriage, you must file this way. For example, if you currently live in Texas, travel to California to be married, and continue living in Texas, you must file your federal tax return as married.
Each state still has its own set of tax laws that must be followed. For tax years 2010, 2011, and 2012, you can file amended federal tax returns if it is beneficial for you.