In general, the Internal Revenue Service allows you to claim your minor children as dependents on your tax return if they live with you for more than half of the year or if you financially support them. But there are other circumstances under which you can claim dependents on your federal tax return. Note that a person may not be claimed as a dependent on more than one person’s federal tax return.
The IRS established criteria to determine who can be claimed as a dependent on another person’s U.S. federal tax return for the purpose of determining income exemptions and tax benefits under the law, such as dependency exemption, the child tax credit, head-of-household filing status, child and dependent care expense credits, exclusions for dependent care benefits and earned income credits.
No one can be claimed as a dependent on a U.S. federal tax return unless they are also a U.S. citizen or a U.S. national or a U.S. resident alien -- or, in certain circumstances, a resident of Canada or Mexico.
Social Security Number
To claim someone as a dependent on a U.S. federal tax return, that dependent must have a Social Security number unless that dependent was your birth child who was born alive during that calendar year and also died during that calendar year and a Social Security number had not yet been applied for. In this case, a copy of the birth and death certificates must be attached as proof of the child's existence.
To claim someone as your dependent, you must have provided at least half of their financial support during the year for which the U.S. federal tax return is being filed. If there is an agreement to the contrary that allows your child’s other parent to claim the child as his or her dependent, even though you provided the majority of the child’s financial support, the agreement takes precedence.
To claim someone as a dependent on your U.S. federal tax return, that person must also have lived with you for more than half the calendar year for which the return is being filed. Exceptions to this are cases, as above, in which your child lives with her other parent and there is an agreement allowing the noncustodial parent to claim the child, or if the child was absent from your home temporarily for school, the military, because of detention in a juvenile facility, for medical treatment, business, vacation purposes, or if this child was abducted by a stranger and therefore is not living with you.
The IRS defines a dependent child as a person who meets the citizenship, Social Security number, income and residency requirements outlined above and is your own natural-born or adopted son or daughter, including a child adopted from another country or a stepchild or a foster child or a brother or sister or a stepbrother or stepsister or a descendant of any of these, or who was either also either under the age of 19 on the last day of the year for which the federal tax return is being filed or was under the age of 24 on the last day of the year for which the federal tax return is being filed and a full-time student or permanently and totally disabled (at any age).
The IRS defines a qualifying dependent relative as a person who meets the citizenship, Social Security number, income and residency requirements outlined above and is your own natural-born or adopted son or daughter, including a child adopted from another country or a stepchild or a foster child or a brother or sister or a stepbrother or stepsister or a descendant of any of these; or your father, mother or an ancestor or sibling of either of them (grandmother, grandfather, aunt, uncle) or stepfather, stepmother, son-in-law, daughter-in-law, father-in-law, mother-in-law, brother-in-law, sister-in-law; or “any other person [other than your spouse] who lived with you all year as a member of your household if your relationship did not violate local law" and who earned less than the personal exemption amount for that year, which, for 2012, was $3,800.