In my practice, two-thirds of my clients in same-sex marriages will actually owe more in taxes by filing as married. So the question comes up often of, will couples in that situation — who properly filed their taxes as unmarried in the past and who benefited from doing so — be REQUIRED to amend those prior years and pay additional taxes?

Based on the IRS guidance issued today, the answer is no. Amending prior years is optional.

Couples who would have benefited from filing as married in prior years can amend (as far back as 2010) if they choose to do so. But amending is optional, not required.

Starting with 2013 returns (and any amended returns filed after September 16 , 2013), couples in same-sex marriages must file as married. But there is no requirement to amend prior years.