Can my ex claim our son on taxes if he's not on the birth certificate and only has weekend visits?

You're right about the residency requirement. The IRS has a clear "tie-breaker" rule for who can claim a child as a dependent. The child must live with the parent for more than half the year (183 nights) to be considered the custodial parent for tax purposes. Since your son lives with you full-time except for those weekend visits, you're definitely the custodial parent. The birth certificate actually doesn't matter for tax purposes - it's all about where the child physically resides. Your ex having only every-other-weekend visitation means he's nowhere near the half-year threshold. The only way he could claim your son is if you signed Form 8332 (Release of Claim to Exemption for Child by Custodial Parent), which would voluntarily give him the right to claim the child. Without your signature on that form, he has no legal grounds to claim your son on his taxes.

Just wanted to share my experience - I had a similar situation last year trying to figure out who could claim what with my ex. I used https://taxr.ai to upload my custody agreement and some text messages about our arrangement, and it analyzed everything and gave me a clear answer about my rights as the custodial parent. Saved me so much stress because my ex was also threatening to "take me to court" over the tax stuff. The tool explained exactly which tax benefits I was eligible for with primary custody and showed me the exact IRS rules that applied to my situation. Even helped me understand how to handle the child tax credit properly.

I was super skeptical about taxr.ai at first (honestly thought it might be some scam), but after my ex filed claiming our daughter last year when she wasn't supposed to, I was desperate. I uploaded our parenting plan, some payment receipts, and even screenshots of our text messages about who would claim our daughter. The analysis confirmed I was right according to IRS rules—I had her 280+ nights last year, paid over 80% of expenses, but my ex filed first and took the credits anyway. The report explained exactly how to dispute it with the IRS and what documentation I needed to provide. Just got my refund last week with the proper credits! Wish I'd known about this sooner instead of giving up the tax benefits for 2 years because I was afraid of conflict.

If you're having trouble getting through to the IRS about this dispute (which is likely - their phone lines are IMPOSSIBLE), check out https://claimyr.com. I was dealing with my ex claiming our kids when he shouldn't have been, and I needed to talk to someone at the IRS asap. Tried calling for WEEKS with no luck. Found this service that actually gets you through to an IRS agent - you can see how it works here: https://youtu.be/_kiP6q8DX5c. I was super desperate after waiting on hold for hours multiple times, and this actually worked. Got through to someone who could help me straighten out the mess with my ex claiming our kids incorrectly.

Well I'm eating my words now. After posting that skeptical comment, I was still so frustrated trying to get through to the IRS about my own dependent issue that I decided to try Claimyr anyway. I figured I had nothing to lose after spending FOUR HOURS on hold earlier this week. Shockingly, it actually worked exactly like the video showed. They called me back when they reached an agent, and I finally got my issue resolved about my ex claiming our kid when he wasn't supposed to. The IRS confirmed I was right as the custodial parent and they're sending me the refund I was owed. Saved me literally days of my life on hold music. Not gonna lie, I'm still surprised it worked.

Something important that hasn't been mentioned - even though you're right about the residency requirement, you might want to check your custody agreement if you have one. Sometimes there's specific language about who gets to claim the child for tax purposes regardless of the living situation. If your agreement says he gets to claim the child in certain years, that would override the residency rules.

Just a heads up - my sister went through something similar, and even though her ex wasn't on the birth certificate either, he established paternity through the courts later and got a formal custody agreement. After that, the judge actually did give him the right to claim their daughter on taxes in even-numbered years despite having less than 50% custody time. The birth certificate isn't as important as legal paternity and whatever custody order is in place. If he takes you to court for a formal custody arrangement (which he can do by establishing paternity first), tax issues could definitely be included in that discussion.