Living Together

• You need to have lived together for the whole tax year to claim your girlfriend as a dependent. If you did not live together for the entire calendar year you are filing for, you cannot claim her. If you've cleared this hurdle, see whether you clear the others.
  
  

Income and Expenses

• As long as your girlfriend has not earned more than $3,650 during the tax year, as of 2010, her financial status qualifies as "dependent." This amount may change year to year, so research current limits before you file. Unemployment benefits count as income, so if your girlfriend made more than $3,650 in unemployment, you cannot claim her. In addition, you must have paid for 50 percent or more of her expenses for the year to claim her as a dependent. In addition, you can only claim her as a dependent if your relationship does not violate local law.
  
  

Tips

• The IRS provides an interactive worksheet you can use to figure out whether a person qualifies as a dependent on a tax return. In general, if you paid for at least half of the food, shelter, medical expenses and necessities for your girlfriend, you've financially supported her and can claim her as your dependent.
  
  

Benefits

• For every dependent you have, you earn an income deduction of $3,650 on your taxes, as of the 2010 tax year. If you and your girlfriend have a child, you would claim two dependents, for an income deduction of $7,300. A dependent girlfriend must still file her own taxes and should answer "yes" to the question asking whether she's being claimed as a dependent.