Now that same sex couples are able to marry in New Jersey (and twelve other states), it is important to understand the tax issues involved.
For example, and as most already know, same sex spouses will be able to file joint federal income tax returns for 2013. There are, however, two additional points of interest. First, the right to file jointly arises from being married in a state which permits same sex marriage, not the state where the couple resides. Secondly, if a same sex couple married prior to 2013, they can amend their prior separate tax returns to joint returns for any tax year still open under the statute of limitations (generally three years from the date the return was filed or two years from the date the tax was paid, whichever is later). A caveat on this is based on Revenue Ruling 2013-17 issued on September 16, 2013 whereby same sex spouses who filed separate 2012 tax returns before September 16 have a choice to amend to a joint return, but those who file for 2012 (or any prior tax year for that matter) after September 16 have no choice; they will generally have to file their 2012 federal income tax return as married filing jointly or married filing separately.
I strongly recommended that you confer with a qualified tax professional if you have any questions or concerns.