In California, same sex couples who were married or Registered Domestic Partners could file married filing joint tax returns going back to 2006. The IRS, following 1996 Federal DOMA, would not allow same sex couples to recognize their relationships at all until a 2012 IRS ruling allowing them to go back to 2008 and amend returns to split income but maintain Single Status.
The new US Supreme Court DOMA holding that the federal government will follow or respect each state and its law on same sex marriage opens up the possibility of amending returns in California and other states allowing same sex marriage to the favored Married Filing Joint Status.
It is time to examine previously filed 1040 federal tax returns to determine if it would be beneficial to have the returns amended to Married Filing Joint Status. Refunds only are allowed going back 3 years so 2010 is the furthest out year to amend returns for a refund. There are other reasons to amend a return than simply getting a refund. Simplicity and favored treatment are two reasons why amending returns to Married Filing Joint makes sense.
When dealing with the IRS in the past on same sex couples with tax issues it was necessary to deal with two separate tax liabilities. That made installment agreements, offer in compromise and of course bankruptcy much more difficult if not impossible. All of those options are going to be available to same sex couples going forward.