As I detailed in another post, the IRS will require same sex married couples to file their income tax returns using the married filing joint returns or married filing separate returns filing status, effective September 16, 2013. http://michaelgraycpa.com/2013/08/30/irs-provides-guidance-for-same-sex-married-couples/
These couples can still file as single persons when they file their 2012 federal income tax return by September 15, 2013. Many married persons experience a “marriage penalty”. This is the last chance for same sex couples to file as single persons, so they should find out if doing so would be to their advantage.
The marriage penalty can apply when the two partners both have earned income. A married person who files a separate income tax return isn’t eligible to claim an IRA contribution. The IRA deduction for a married partner whose spouse is a participant in a qualified retirement plan (including a 401(k) plan) can be phased out. A married person who files a separate income tax return isn’t eligible for the adoption credit.
The devil is in the details. You have to work through the details of your personal situation with a tax advisor.
There are only two weeks left before the deadline, and many tax return preparers are struggling to finish their business tax returns and make 2013 estimated tax reviews by September 16. Good luck getting an appointment with a good tax advisor!