The maximum age to claim a child as a dependent depends on their situation. In most cases, a child must be under 19 at the end of the tax year. If they’re a full-time student, that ceiling rises to under 24. And if they’re permanently and totally disabled, there’s no age limit at all. One important catch: the Child Tax Credit uses a stricter cutoff of under 17, so an older dependent still counts as your dependent but no longer generates that credit.
The Default Rule: Under 19
To be your qualifying child, the child must be under 19 at the end of the tax year and younger than you (or your spouse, if you file jointly).1Office of the Law Revision Counsel. 26 U.S. Code 152 – Dependent Defined Age is measured on December 31. A child whose 19th birthday falls on the last day of the year has already turned 19 by the close of the year and no longer meets the test.
Age is one of several tests. The child also has to be related to you (son, daughter, stepchild, foster child, sibling, half-sibling, stepsibling, or a descendant of any of them, such as a grandchild, niece, or nephew), live with you for more than half the year, and not provide more than half of their own support.2Internal Revenue Service. Qualifying Child Rules Time away for school, medical treatment, or military service still counts as time lived with you. The child also cannot file a joint return with a spouse, unless the return was filed only to claim a refund of withheld taxes.3Internal Revenue Service. Dependents
Full-Time Students: Under 24
If your child is a full-time student, the age ceiling moves to under 24 at the end of the tax year.1Office of the Law Revision Counsel. 26 U.S. Code 152 – Dependent Defined The student must be enrolled for whatever course load the school considers full-time, and they need to have carried that load during some part of at least five calendar months of the year.4IRS.gov. Full-Time Student The five months don’t have to be consecutive; a spring semester and a fall semester with a summer break in between satisfy the requirement.
The school can be a college, university, trade school, or any institution with a regular teaching staff, a set curriculum, and enrolled students. On-farm training courses offered by a state or local government agency also count. The detail that catches families off guard: a 24-year-old college senior whose birthday falls before December 31 no longer qualifies, even if they were a full-time student all year.
Permanently and Totally Disabled: No Age Limit
A qualifying child who is permanently and totally disabled has no age limit.1Office of the Law Revision Counsel. 26 U.S. Code 152 – Dependent Defined A person meets that definition if a physical or mental condition prevents them from doing any substantial work, and a physician determines the condition has lasted or is expected to last at least 12 continuous months or to result in death. A 40-year-old adult child living at home who meets this standard can still be your qualifying child, so long as the relationship, residency, and support tests are also satisfied.
Why the Child Tax Credit Stops at 17
This is where many parents get tripped up. Even though your child can remain your dependent through age 18 (or 23 as a student), the Child Tax Credit uses its own, stricter cutoff: the child must be under 17 at the end of the tax year.5Internal Revenue Service. Child Tax Credit That requirement sits in a separate section of the tax code from the general dependency rules.6Office of the Law Revision Counsel. 26 USC 24 – Child Tax Credit
For the 2025 tax year (filed in 2026), the maximum Child Tax Credit is $2,200 per qualifying child under 17, following the increase enacted by the One Big Beautiful Bill Act. Up to $1,700 of that amount is refundable, meaning you can receive it even if your total tax bill is zero.7Internal Revenue Service. Refundable Tax Credits Both amounts are now indexed for inflation, so they may rise slightly for 2026. The credit starts phasing out once your adjusted gross income exceeds $200,000 ($400,000 for married couples filing jointly), shrinking by $50 for every $1,000 above those thresholds.
A 17-year-old dependent or a 20-year-old college student you claim as a qualifying child won’t generate the $2,200 credit. They may instead qualify you for the $500 nonrefundable Credit for Other Dependents.
When an Older Child Becomes a Qualifying Relative
Once a child ages out of the qualifying child rules, you can often still claim them under the separate “qualifying relative” category, which has no age test at all. Three conditions apply:
- The person’s gross income for the year must fall below the annual threshold. For the 2025 tax year, that limit is $5,200. For the 2026 tax year, it rises to $5,300.8Internal Revenue Service. 1040 (2025) Instructions
- You must provide more than half of the person’s total financial support for the year.
- The person cannot be anyone’s qualifying child.
The qualifying relative category doesn’t unlock the Child Tax Credit, but it does entitle you to the $500 Credit for Other Dependents, and it may affect your eligibility for head-of-household filing status.
Citizenship and Social Security Number
Age isn’t the only limit worth knowing about. Whatever their age, a dependent must be a U.S. citizen, U.S. national, U.S. resident alien, or a resident of Canada or Mexico.3Internal Revenue Service. Dependents For the Child Tax Credit specifically, the child must also have a valid Social Security number issued before the due date of the return.5Internal Revenue Service. Child Tax Credit
What Each Age Unlocks
Different credits use different age lines, so it helps to see them side by side:
- Under 13: Eligible for the Child Tax Credit ($2,200), the Child and Dependent Care Credit for daycare or after-school expenses, and the EITC qualifying child rules.9Internal Revenue Service. Child and Dependent Care Credit Information
- Ages 13 to 16: Still eligible for the Child Tax Credit and EITC qualifying child rules, but the dependent care credit no longer applies unless the child is disabled.
- Ages 17 to 18: Too old for the CTC. Qualifies for the $500 Credit for Other Dependents and still counts as a qualifying child for EITC purposes if living with you.2Internal Revenue Service. Qualifying Child Rules
- Ages 19 to 23 as a full-time student: Qualifies for the $500 Credit for Other Dependents and the EITC qualifying child rules. May also make you eligible for education credits like the American Opportunity Tax Credit.
- Age 24 or older (or 19 or older and not a student): No longer a qualifying child. May be claimed as a qualifying relative if the income and support tests are met, generating the $500 Credit for Other Dependents.
- Permanently disabled at any age: Remains a qualifying child with no age limit, potentially eligible for the CTC (if under 17), EITC, and dependent care credit.
The practical takeaway: your child likely stops generating the Child Tax Credit long before they stop being your dependent. Planning around both dates, rather than assuming they’re the same, is what keeps the return accurate.