Amend Past Year Returns
Married same-sex couples may want to consider amending previous years' tax returns if it will be financially beneficial — and it certainly could be, given the recent requirement to file joint tax returns.
In general, any taxpayer can amend past federal tax returns going back three years. For same-sex married couples, this might be particularly advantageous now that they may file as married. For example, it could net a refund for couples that previously paid after-tax health insurance premiums or who missed out on other tax deductions or credits, like the Earned Income Tax Credit.
For example, a same sex couple legally married before 2009 — but unable to file as married because of federal tax limitations — may want to consider filing an amended return for tax years 2010, 2011 and 2012, enabling them to receive any refunds that may now be owed to them.
While you aren't required to amend your returns, you may want to recalculate them to see if doing so will offer a refund or other tax advantages. Generally, if one spouse was the primary earner, filing an amended return will work in your favor [source: Lankford].