Can my sister claim me as a dependent if I am over 25?

[xmasbaby0]

If you had less than $4300 of income in 2020--NOT counting Social Security--and she paid for over half your support she might be able to claim you as a dependent.  All she "gets" is the $500 credit for other dependents for claiming you.  Or if she paid your medical expenses she might be able to enter those as an itemized deduction.

IRS interview to help determine who can be claimed:

https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent

https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent 

If you CAN be claimed as a dependent on someone else's tax return then if you prepare a tax return for yourself you have to say on your own return that you can be claimed as a dependent.

[DoninGA]

You must meet all the Qualifying Relative rules for her to claim you as a dependent.

To be a Qualifying Relative -

1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross income for the year must be less than $4,300 (social security does not count) in 2020
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen or a U.S., Canada, or Mexico resident for some part of the year.
6. The person must not file a joint return with their spouse.