Qualifying child rules
A child counts for the Child Tax Credit only if every one of the IRS tests passes. Missing a single test moves the child out of the CTC — sometimes into the $500 Credit for Other Dependents, sometimes out of both credits. The tests are: age, relationship, residency, support, dependency, citizenship or residency, the SSN rule, and the joint-return rule.
- Age: under 17 at the end of the tax year — a child who turns 17 during the year does not qualify for that year's CTC.
- Relationship: son, daughter, stepchild, eligible foster child, sibling, half-sibling, step-sibling, or a descendant of any of these.
- Residency: lived with you for more than half of the tax year (temporary absences for school, medical care, or military service still count).
- Support: the child did not provide more than half of their own support during the year.
- SSN: a valid-for-employment SSN, issued by the return's due date including extensions.
The tests, one by one
Age. The child must be under 17 at the end of the tax year. A child who turns 17 on December 31 does not qualify for that year — but may qualify for the $500 Credit for Other Dependents instead, if its tests are met.
Relationship. The child must be your son, daughter, stepchild, eligible foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, or a descendant of any of these (for example, a grandchild or niece). An adopted child counts as your child, including a child lawfully placed with you for adoption.
Residency. The child must have lived with you for more than half of the tax year. Time away at school, in hospital, on a family holiday, or on military service counts as living with you — these are temporary absences. A child born during the year counts as living with you for the whole year if your home was the child's home; a child who died during the year counts if the child lived with you for more than half the part of the year before death.
Support. The child must not have provided more than half of their own support during the year. Support includes food, housing, clothing, education, medical care, and recreation. A teenager with a part-time job rarely fails this test; a child supporting themselves on full-time earnings can.
Dependency and citizenship. You must claim the child as your dependent, and the child must be a US citizen, US national, or US resident alien. A child who files a joint return generally disqualifies the claim, unless the joint return was filed only to claim a refund of withheld tax or estimated payments.
The tie-breaker: when two people can claim the same child
Only one person can claim a child for the CTC. If two people could — most often separated parents — the IRS tie-breaker decides. Between parents, the child goes to the parent the child lived with longest; if equal, the parent with the higher adjusted gross income. Between a parent and a non-parent, the parent wins if the parent's AGI is higher than the non-parent's; otherwise the non-parent with the highest AGI can claim. A written agreement between parents does not override the tie-breaker for the CTC unless Form 8332 is used — see shared custody and special cases.
The SSN rule for the child
Each qualifying child must have a Social Security number valid for employment, issued before the due date of your return including extensions. An ITIN is not enough for the CTC, even if the child is otherwise a dependent. This is the single most common reason a CTC claim fails on an otherwise valid return: the child's SSN was applied for late, or the return was filed before the number arrived. If the SSN arrives after the due date including extensions, the child cannot be a qualifying child for that year — but check the Credit for Other Dependents, which has separate identification rules.
Sources to check: IRS, Child Tax Credit (irs.gov); IRS Taxpayer Advocate Service, Claiming the Child Tax Credit or Credit for Other Dependents; IRS Publication 501.