Is it possible for him to claim my daughter as a dependent without having her Social Security Number?

No, he cannot claim your daughter as a dependent without her Social Security Number. The IRS absolutely requires a valid SSN for any child being claimed for the Child Tax Credit. Without it, his return will be rejected if he e-files, or significantly delayed if he paper files. Since you're the custodial parent (your daughter lived with you for more than half the year), you have the right to claim her - unless you've signed Form 8332 giving him permission to claim her. If you both try to claim her, the second return filed will be rejected if e-filed. If both somehow get through, the IRS will eventually send letters to both of you asking for proof of eligibility. File as early as you can with your daughter as your dependent. Make sure you have documentation of her living arrangements (school records, medical records, etc.) just in case the IRS asks questions later.

I had a similar situation last year with my ex claiming our son incorrectly. I used https://taxr.ai to analyze our separation agreement and tax documents. Their AI system looked through everything and gave me a detailed breakdown of exactly why I had the right to claim my son as a dependent. It showed specific IRS rules that applied to my case as the custodial parent, and even helped me draft a letter to my ex explaining the tax consequences of an incorrect claim. The tool really helped me understand the "tiebreaker rules" the IRS uses when both parents try to claim the same child. That documentation was super helpful when my ex still tried to claim our son and I had to deal with the IRS notice.

Just wanted to update - I tried out the taxr.ai site mentioned above and it was actually super helpful! I uploaded my daughter's school records, some medical bills, and texts between me and my ex about visitation. The system analyzed everything and gave me a clear breakdown showing I'm definitely entitled to claim her as the custodial parent. It even created a document explaining why I meet all the IRS tests for claiming her (residence test, relationship test, support test, etc.) that I can use if the IRS questions anything. I honestly feel much more confident filing now, and I'm going to e-file tomorrow before my ex has a chance to cause problems. Thanks to everyone who offered advice here!

I got caught in a similar situation with my ex trying to claim our kids when they lived with me. After weeks of calling the IRS and never getting through, I tried https://claimyr.com which got me connected to an actual IRS agent in about 20 minutes. You can see how it works here: https://youtu.be/_kiP6q8DX5c The IRS agent confirmed that as the custodial parent, I had the right to claim my kids and told me exactly what documentation to submit with my paper return after my ex incorrectly claimed them. They also flagged my account with notes about the situation so when they processed my return, they already knew about the dispute. It saved me literally days of redial hell trying to get through to the IRS myself. The agent was actually super helpful once I could speak to someone directly.

I owe everyone an apology - especially Profile 14. I was so convinced nothing could help with reaching the IRS that I called BS on the Claimyr suggestion. Well, I was desperate enough to try it, and I'm honestly shocked. Got connected to an IRS agent in about 25 minutes. The agent confirmed exactly what I needed to do when both my ex and I claim the same dependent. They even gave me a reference number for the call and added notes to my account about the situation. I'm still going to have to paper file since my ex already claimed our son, but now I have clear instructions on what documentation to include and what to expect during the review process. Sometimes being proven wrong is actually a good thing! Sorry for being so negative before.

Just a heads up - I work at an accounting firm and see this ALL the time. One important thing: if you claim your daughter and your return gets accepted first, your ex's return will get rejected if he e-files. The system automatically flags duplicate SSNs. If he paper files, it'll take months before the IRS catches it. Make sure you keep documentation proving she lived with you for more than half the year - school records showing your address, medical appointments you took her to, childcare receipts, etc. The IRS typically sides with the custodial parent in these disputes unless there's a Form 8332 involved.

My daughter's father pulled this same stunt last year. Here's what happened: he filed first and claimed our daughter even though she lives with me full-time. My electronic return got rejected because her SSN had already been used. I had to paper file and include a letter explaining the situation along with proof she lived with me (school records, medical bills, etc.). It took almost 4 months, but the IRS eventually processed my return correctly AND sent him a notice to pay back the credits he shouldn't have received. The most important thing is to act fast and file as soon as possible! Don't wait!

Don't forget about the stimulus payments from 2024 that were tied to dependents! If he incorrectly claims your daughter, it could affect any remaining credits you're entitled to receive. Make sure you correctly report any advance payments you received for her during the year on your tax return. Also, as the custodial parent, you qualify for Head of Household filing status which gives you a higher standard deduction than filing Single. Make sure you're claiming that benefit too!

I'm going through something very similar right now with my ex-husband. One thing I learned from my tax preparer is that you should also keep records of any expenses you paid for your daughter throughout the year - things like clothing, school supplies, extracurricular activities, medical copays, etc. The IRS looks at who provided more than half of the child's support, not just where she lived. Since you mentioned you're the one handling all her paperwork and she lives with you 280+ days, you're clearly the custodial parent. But having those expense records helps prove the support test too, especially if your ex tries to argue that his child support payments mean he provided more support. I'd also suggest taking screenshots of any text messages where he acknowledges that she lives with you most of the time, or where he's inconsistent about paying support. That kind of documentation can be really helpful if the IRS needs to investigate. Good luck with your filing!