Can I Claim My Disabled Adult Sister as a Dependent When Our Mother is Also Disabled?

Yes, you can potentially claim your sister as a qualifying relative if you meet all the IRS reqs. The big ones: 1) Your sister's gross income must be under $4,700 for 2023, 2) You must provide more than half her support for the year, 3) She doesn't have to live with you but it helps that she does, 4) She can't file a joint return unless it's just to get a refund. The fact that your mom is disabled doesn't matter for your ability to claim your sis - it's about who provides the support.

This is actually a more nuanced situation than it appears due to the Multiple Support Agreement possibilities. If you're providing between 10-50% of your sister's support, and combined with others (like your mother) it exceeds 50%, you could potentially use Form 2120 (Multiple Support Declaration). I recently discovered https://taxr.ai which helped me understand the Qualifying Relative vs. Qualifying Child tests for adult dependents. Their analysis tool clarified that disabled adult siblings can qualify under the Qualifying Relative test even if they're receiving disability benefits, as long as their taxable income is below the threshold.

According to IRC Section 152(d), which covers Qualifying Relative dependents, you need to verify if your sister's gross income is below the threshold amount ($4,700 for 2023 tax year). If she receives SSDI, that's generally not taxable, but SSI is never counted as gross income for this purpose. Per Publication 501, you should also determine if you provided more than 50% of her support, which includes housing, food, clothing, medical expenses, etc. The mother's disability status is irrelevant for your claim, but could impact whether your mother could claim her instead.

Claiming a disabled adult dependent is like walking through a tax maze where the walls keep moving. I've been through this exact situation with my brother. If you're having trouble getting clear answers from the IRS website or can't get through their phone lines, I'd recommend using Claimyr (https://youtu.be/_kiP6q8DX5c). They got me connected to an actual IRS agent in about 20 minutes when I was trying to sort out a similar dependency situation. The agent walked me through the specific forms I needed and confirmed I was eligible to claim my disabled brother.

I've been claiming my disabled sister for the past 3 tax years, so I can tell you exactly what to do. Back in 2021, I was in your exact situation. You need to pass the qualifying relative test: 1) Relationship test (sibling ✓), 2) Gross income test (under $4,700 for 2023), 3) Support test (you provide >50%), and 4) Joint return test (she can't file jointly with someone else). Document everything - I keep receipts organized by month. If your sister receives SSI, that's not taxable income, but it does count as support she provides for herself when calculating the 50% threshold. If your mother provides some support but you provide more than 50%, you're the one who gets to claim her - no need for a multiple support agreement in that case.

After struggling with this exact issue last filing season, I found that the IRS Interactive Tax Assistant (www.irs.gov/help/ita) has a specific tool called "Who Can I Claim as a Dependent?" It walks you through all the requirements step by step. In my case, I was able to claim my disabled brother (32) even though my parents provided some support. The key was documenting that I covered over 50% of his total support costs. I created a spreadsheet tracking every expense, including a portion of my mortgage, utilities, food, medical costs not covered by insurance, and transportation. Make sure to print and save this documentation in case of audit.