Under 19 Years of Age
If your child meets the other tests, he must not be older than you or, if married and filing a joint return, your spouse. He does not have to be a student to qualify as long as he is under the age of 19 as of Dec. 31 of the year for which you are filing taxes.
Aged 19 through 23
A child younger than 24 years of age as of Dec. 31 of the tax year in question may still qualify as a dependent if she is a full-time student. She may attend high school, a college or university or a technical school as long as she attends for at least the minimum hours the school considers full-time. Schools that provide classes only by correspondence or online are not eligible. She must be in class for at least some portion of any five calendar months, which are not required to be consecutive. A child must not be older than you or your spouse if you file a joint return.
If the child is totally and permanently disabled, the IRS does not limit his age. He must not be capable of performing any gainful work due to a mental or physical impairment and receive certification from a physician that his condition is expected to last a minimum of one year or is expected to be fatal.
A qualifying child must meet the test for relationship, which allows you to claim a natural child, foster child, stepchild, sibling, step-sibling or a child descended from one of these classifications. The child must have resided in your home for at least 51 percent of the year, with special exceptions available for parents who are separated or divorced or whose child was kidnapped, died or born during the year. Children away from home due to education, military duty or illness may still meet the residency test. The child must provide less than half of her own support during the year. If the child is married, she must not file jointly with her spouse unless the return is filed for the sole purpose of receiving a refund.