Beginning in 2013, same-sex married couples can file jointly and claim their dependents, just as heterosexual married couples have been able to do for years. Being able to claim a dependent can make a big difference on a couple's federal income tax bill. For starters, it reduces the amount of taxable income and the overall tax liability. In tax year 2015, for example, simply claiming a qualified dependent on your federal income taxes will gain same-sex married couples filing jointly an exemption up to $4,000.
According to the IRS, a dependent is someone for whom you provide support who is either under the age of 19 or who is a full-time student up to age 24. During the tax year, you'll need to have provided more than half the support to this child, who also needs to have lived with you for a significant period. Qualifying dependents include your child, a sibling, stepsibling or another relative. Foster children also are eligible. Keep in mind that if a same-sex couple decides to go the married filing separately route, only one can claim the child [sources: Cussen, Morah].