From Think Progress:
Those savings would come from numerous sources. Tax revenues would rise by more than $400 million a year, and though costs on programs like Social Security and federal benefits would increase, costs for safety net programs like Medicare, Supplemental Security Income, Medicaid, and other programs would go down.
That’s significant, because the largest benefit from recognizing same-sex marriages comes from what it would do for individual couples and families. Same-sex couples aren’t allowed to file joint taxes, which prohibits them from claiming some tax credits and deductions that would benefit their families. They also aren’t eligible for spousal health, Social Security, or federal pension benefits, making it harder for some LGBT families to make ends meet. Older LGBT couples are more likely to live in poverty than married heterosexual seniors, which is why ending DOMA would reduce costs for programs like Medicaid and SSI — access to spousal benefits would lift many LGBT Americans out of poverty and off of the social safety net.