You can claim your sister as a dependent on your taxes if she meets every requirement under one of two IRS categories: qualifying child or qualifying relative. Which category applies depends mostly on her age. A younger sister who lives with you generally goes through the qualifying child tests; an adult sister goes through the qualifying relative tests, where her income and how much of her support you paid do most of the work.
A successful claim is worth real money. Depending on her situation, you may unlock the Child Tax Credit of up to $2,200, the $500 Credit for Other Dependents, head of household filing status, or the Earned Income Tax Credit.1Internal Revenue Service. Child Tax Credit
Which Path Applies to Your Sister
She only needs to qualify under one category, but she must pass every test within it. Failing one test disqualifies her under that category, though she may still fit the other one.2Internal Revenue Service. Dependents
The qualifying child path fits a sister who is under 19, or under 24 and a full-time student, or permanently and totally disabled at any age. The qualifying relative path is how most people claim an adult sister, and it turns on her gross income and your financial support rather than her age.
Both paths share baseline rules. Your sister must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.2Internal Revenue Service. Dependents She cannot file a joint return with a spouse unless the sole purpose was to claim a refund of withheld or estimated taxes.3Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information And if someone else could claim you as their dependent, you cannot claim anyone at all.4Internal Revenue Service. Dependents
Qualifying Child Rules
Five tests apply. Your sister, stepsister, or half-sister automatically satisfies the relationship test, as does a descendant of any of them.2Internal Revenue Service. Dependents
- Age: under 19 at year-end, or under 24 if she was a full-time student. Neither limit applies if she is permanently and totally disabled, meaning she cannot do substantial work because of a condition expected to last at least 12 continuous months or result in death.
- Residency: she lived with you more than half the year. Temporary absences for school, medical care, or military service still count as time with you.
- Self-support: she did not provide more than half of her own support during the year. If she was working and paying her own way, this test fails.5Office of the Law Revision Counsel. 26 U.S. Code 152 – Dependent Defined
- Joint return: she did not file jointly with a spouse (refund-only exception aside).
Qualifying Relative Rules
This is the path for an adult sister. Four tests apply, and the financial ones decide most cases.
Not a qualifying child of anyone else. If your sister could be claimed as a qualifying child by a parent, for instance because she is under 24, a full-time student, and living at home, you cannot claim her as a qualifying relative.
Gross income under the annual limit. For 2026, her gross income must be below $5,050.2Internal Revenue Service. Dependents Gross income means taxable wages, self-employment income, taxable interest, rental income, and the like. It does not include tax-exempt items such as certain Social Security benefits. A dollar over the threshold disqualifies her, no matter how much you spent on her.
Relationship. Sister, stepsister, and half-sister all qualify automatically, and she does not have to live with you for this path.3Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
Support. You provided more than half of her total support for the calendar year.3Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
How the Support Test Actually Works
The support test compares what you spent on your sister to the total spent on her by everyone, including her own contributions. Your share has to exceed 50%.
Countable expenses include housing, food, clothing, medical and dental care, education, transportation, and recreation. Housing is usually the largest number, valued at the fair rental value of the space she occupies plus a reasonable share of utilities. If she lives with you rent-free, the fair market rent for comparable housing in your area is what counts as your contribution.
Anything she spent on herself goes in her column. That includes wages she used for her own food or clothing, savings she drew down, Social Security benefits, and government benefits like Supplemental Security Income. The question is simple to state and harder to document: of every dollar spent to keep her housed, fed, clothed, and cared for during the year, did more than half come from you?
When Several Relatives Share the Cost
If no single person paid more than half but the family collectively did, one of you can still claim her using a multiple support agreement on Form 2120.6Internal Revenue Service. About Form 2120, Multiple Support Declaration The group must have provided more than half of her support together, and the person claiming her must have personally contributed more than 10%. Every other contributor above 10% signs a written statement agreeing not to claim her that year, and you attach Form 2120 to your return.7Internal Revenue Service. Form 2120 (Rev. December 2025) – Multiple Support Declaration The group can rotate the claim year to year. Every other qualifying relative rule still applies, including the gross income limit.
When Someone Else Has a Stronger Claim
If your sister meets the qualifying child test for more than one person, tie-breaker rules decide who gets to claim her.8IRS.gov. Tie-Breaker Rule
- A parent beats a non-parent. If your sister’s parent could claim her, you as a sibling cannot, even if she lived with you longer.
- Between two parents not filing jointly, whichever parent she lived with longer wins; if equal, the higher AGI wins.
- Between two non-parents, the higher AGI wins. This is the rule that decides between siblings.
- If a parent could claim her but chooses not to, you can claim her only if your AGI is higher than that parent’s.
Talk to your family before filing. Two people claiming the same dependent triggers an IRS notice and holds up both returns.
What Claiming Her Is Worth
The benefits available depend on her age and which category she falls under.
Child Tax Credit. If she is a qualifying child and under 17 at year-end, you can claim up to $2,200. Up to $1,700 is refundable through the Additional Child Tax Credit if you have at least $2,500 in earned income. The credit phases out starting at $200,000 of modified AGI, or $400,000 for joint filers.1Internal Revenue Service. Child Tax Credit
Credit for Other Dependents. If she is 17 or older, or qualifies only as a qualifying relative, you get the $500 non-refundable Credit for Other Dependents instead.9Internal Revenue Service. Parents – Check Eligibility for the Credit for Other Dependents
Head of household. If you are unmarried and paid more than half the cost of keeping up a home where your dependent sister lived for more than half the year, you can file as head of household.3Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information For 2026, that carries a $24,150 standard deduction against $16,100 for single filers, plus wider brackets.10Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill
Earned Income Tax Credit. If she is your qualifying child, she can also make you eligible for the EITC. For 2026, the maximum credit with one qualifying child is $4,427, phasing out completely at $51,593 for single or head of household filers and $58,863 for joint filers. For EITC purposes only, she must also be younger than you.11Internal Revenue Service. Qualifying Child Rules
Medical expenses. Bills you paid for her can go into your itemized medical expense deduction if they, combined with your other qualifying medical costs, exceed 7.5% of your AGI. The IRS also lets you deduct medical expenses for someone who would have been your dependent except that they exceeded the gross income limit or filed a joint return, so this deduction can still be available even if the dependency claim itself is not.12Internal Revenue Service. Publication 502 (2025), Medical and Dental Expenses
Documents to Keep in Case the IRS Asks
The burden of proof is on you. If the IRS questions the claim, it sends Form 886-H-DEP asking for supporting documents.13Internal Revenue Service. Form 886-H-DEP Supporting Documents for Dependents
For the relationship, birth certificates or other official documents showing the family link. For residency under the qualifying child test, school records, medical records, or a letter on official letterhead from a school, doctor, social services agency, or place of worship showing her name, your shared address, and the dates she lived there. Documents signed by a relative do not count.
For the support test, keep the paper trail: a rental agreement or documentation of fair rental value, utility bills with cancelled checks, medical bills and receipts, clothing receipts, and statements from any agency paying benefits to your sister. A monthly spreadsheet backed up by receipts is the cleanest way to show you covered more than half. Start on January 1; reconstructing a full year at tax time is where these claims fall apart.