The Internal Revenue Service (IRS) allows you to take a tax deduction for each qualifying child or other relative you support. The IRS has very specific definitions of who qualifies as a dependent for tax purposes. You can claim one deduction for each dependent you have.
The IRS is clear on several situations where you cannot claim a dependent:
The person is not related to you.
You or your jointly filing spouse is claimed as a dependent by someone else.
Your dependent is married, filing jointly, and has tax liability on his or her own return.
The person is not a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico for at least some part of the tax year. Exceptions are allowed for adopted children.
Examples of a qualifying child include your child, adopted child, foster child, stepchild, half sibling, sibling, or a descendant of any of these. The child must be under age 19 at the end of the year, or a full-time student younger than 24, or if permanently disabled they can be any age. The child must have lived with you more than half the year and must not have provided more than half his or her financial support.
In the case of divorced parents, generally the custodial parent is entitled to claim the child as a dependent. A child who is born or dies during the year counts as a dependent that year.
Qualifying relatives may be older or not living with you. They can be a qualifying relatives if their gross incomes are less than $3,400 and you continue to provide more than half their support. Note that this income limit is subject to change. No age test is required for a qualifying relative.
If your dependent is a qualified child or qualified relative, you must include a valid social security number, individual taxpayer identification number, or adoption taxpayer I.D. for each dependent you claim. This allows the government to verify the existence of your dependent.
If you intentionally claim someone you know does not legally qualify as a dependent, you will likely owe the IRS additional taxes. You may also owe fines or penalties, or be charged with tax fraud.