Although older teenagers may not want to believe it, they generally don't automatically become "adults" when they turn 18 -- at least in the realistic sense of the word. In many cases, they still need Mom and Dad to provide for them or at least to help them make ends meet. In turn, parents sometimes get to claim their college-age children on their tax returns, but several factors must line up to make this possible.
Your Child Must Go to School
You have two options for claiming a dependency exemption for your child on your tax return: He must meet the tax code criteria as a qualifying child or he must do so as a qualifying relative. As your qualifying child, it's not enough that he's old enough to go to college. He must actually do so. If he's not enrolled full time during some portion of at least five months of the tax year, you can't claim him as a dependent past the year he turns 19. The five months don't have to be consecutive. If he's a student, you can claim him until the year in which he turns 24. The age rules and the school requirement don't apply to children who are permanently disabled. You can claim a deduction for them as long as they meet Internal Revenue Service rules for disability.
Other Qualifying Child Rules
Your child's primary residence must be with you for more than six months of the year if you're going to claim him as a qualifying child. The time he spends away at school doesn't count as living elsewhere but as a temporary absence. The IRS says you must pay at least 50 percent of his living expenses. If your mortgage is $1,500 a month and you have a family of four, $375 a month goes to your child's share. You would also attribute to him 25 percent of things like your grocery bill when he's home and utility payments, plus clothing you purchase for him and uninsured medical costs. Even if he pays something toward these expenses, you've got this rule covered if his contributions don't exceed 50 percent of the total. It's OK if he has a job and earns money of his own, and it's fine if he contributes something toward his own expenses, provided that he's not using his money to pay for more than half his own support.
Divorced and Separated Parents
If you and your child's other parent are no longer married or living together, this doesn't change the rules for a qualifying child but it does add a wrinkle or two. Typically, only the custodial parent can claim him because he would live with that parent more than half the year. If he lived with both of you an equal amount of time -- six months in each home -- the parent with the highest adjusted gross income has the right to claim him. You and your ex must together pay for at least half his support.
Claiming Your Child as a Qualifying Relative
If your child doesn't meet all these rules, you might still be able to claim him as a qualifying relative. In this case, he doesn't have to live with you for half the year. He can have his own residence as long as you're paying half or more of his living expenses. Nor does it matter how old he is. However, his total income cannot exceed $3,950 as of 2014 -- the amount of the dependency exemption you want to claim. Whether he qualifies as your child or as a relative, he can't claim a personal exemption for himself on his own tax return. He can't claim a dependent of his own and he can't file a joint return if he happens to be married.