Recognition

• Due to the Defense of Marriage Act, the federal government only recognizes marriages between one man and one woman, and does not confer the benefits reserved for married couples on couples in marriage-like arrangements, such as domestic partnerships and civil unions. The IRS is part of the federal government and does not recognize domestic partnerships for tax purposes.
  
  

Dependents

• Individuals can claim dependents unrelated to them, such as a domestic partner, if all of the following requirements are met: the dependent lived in the tax payer's household during the tax year in question, the tax payer paid more than half of the dependent's expenses for the tax year in question and the dependent did not make more than a specified amount. This amount was $3,650 in 2009, though it changes annually.
  
  

California and Oregon

• California and Oregon allow domestic partners to file jointly on state taxes like a married couple. In these states, domestic partners can also deduct the cost of health insurance from their taxable income. More states may be added to this list in the future, since state laws regarding domestic partnerships change every legislative session.
  
  

Other States

• In the other 48 states, domestic partners must file separately either because the state does not recognize the relationship, does not recognize the relationship for tax purposes -- such as Colorado -- or does not have state income taxes -- as in the case of Washington, which has a comprehensive domestic partnership law.
  
  

Tax Tips

• Domestic partners should keep thorough records of who pays for what, leave plenty of time to discuss and strategize taxes and approach taxes as a unit, recommends Tina Salanda, CPA, in an article for the New York Times. Partners can be strategic about deciding who claims head of household status and tax credits, and can take advantage of being in lower tax brackets as individuals than they would be were they to file jointly.