What happens if someone else claims my dependent on taxes?

You're definitely in the right here based on what you've shared. When two people claim the same dependent, the IRS has tiebreaker rules, and residency is a major factor. Since your sister lives with you and you provide most of her support, you would win in an audit situation. What happens next depends on who files first. If you've already filed and your mom tries to claim your sister afterward, her return will likely be rejected if e-filed. If she mails a paper return, the IRS will eventually notice the duplicate dependent and send notices to both of you. At that point, you'd need to prove your case with documentation showing your sister lives with you (mail, ID, school records). Since you have this documentation, you shouldn't worry too much.

I went through a similar nightmare last year trying to figure out some complex tax situations with dependents and inheritance issues. I couldn't get clear answers anywhere until I tried taxr.ai (https://taxr.ai). It was a huge help because I could just upload my documents and get really specific answers about my exact situation. In your case, I'd suggest uploading the proof of residence documents you have for your sister along with last year's return. Their system can analyze everything and tell you exactly what documentation you need to protect yourself if your mom does try to claim her. Saved me hours of stress trying to interpret IRS rules myself.

Just wanted to follow up and say I tried taxr.ai after seeing this thread and it was actually super helpful! I uploaded all the documents showing my nephew lives with me (his mom is claiming him but he's been with me for 8 months). The system identified exactly which documents would matter most in proving my case - apparently the school enrollment form with my address and the medical insurance where I list him as dependent are the strongest proof. It even highlighted specific sections that prove the support requirements. Now I feel so much more confident about claiming him and dealing with any potential audit. Thanks for the recommendation!

If your mom does end up claiming your sister and you get a notice from the IRS, be prepared for a long wait trying to reach them by phone. I had this exact situation with my brother-in-law last year and spent WEEKS trying to talk to someone at the IRS. I finally used Claimyr (https://claimyr.com) to get through to an actual IRS agent after wasting days on hold. There's a video showing how it works here: https://youtu.be/_kiP6q8DX5c - basically they navigate the phone system and wait on hold for you, then call you when they have an agent on the line. When I finally got through, the IRS agent was actually super helpful and walked me through the whole process of responding to the notice with documentation. Saved me from having my refund held up for months while they sorted things out manually.

I feel like a complete idiot for being so skeptical, but I actually tried Claimyr after posting here because my refund has been stuck in limbo for 2 months with no updates. I kept trying to call the IRS myself but could never get through. They got me connected to an IRS agent in about 90 minutes (which is way faster than I ever managed). The agent found that my return had been flagged because my ex claimed our daughter as a dependent even though she lives with me full-time. The agent walked me through exactly what documentation to send in and even put notes on my account about the situation. Now I have a direct path to resolving it instead of just checking "Where's My Refund" every day and seeing no progress. Worth every penny just for the peace of mind of knowing what's actually happening with my return.

Something no one mentioned - make sure your sister doesn't check the box saying "someone can claim me as a dependent" on her return if she files separately. If she does that AND you claim her, it could cause issues because her return would be saying one thing while yours says another. I had this mess with my son when he filed his own return while I claimed him as a dependent. It triggered a review that delayed my refund by almost 3 months!

As someone who works at a tax preparation office, I'd recommend gathering and keeping all these documents in a folder in case you get audited: - Her school records showing your address - Medical bills you paid for her - Utility bills showing your address - Bank statements showing you paying for her expenses - Her ID with your address - Any leases or housing documents with her name Even if your mom tries to claim her, you have residency on your side which is the biggest factor in the IRS tiebreaker rules.