Will filing a tax extension lock in my dependent claims when filing MFS?

The extension doesn't actually lock in your dependent claims - it only extends your filing deadline. What determines who can claim the children is primarily who qualifies as the custodial parent under IRS rules, not who files first. As the custodial parent, you generally have the right to claim the children unless you've signed Form 8332 releasing that right to your ex. Even if your ex files first and incorrectly claims the children, you can still claim them on your return if you're legally entitled to do so. If both you and your ex claim the same dependents, the IRS will likely flag both returns and may request additional documentation to determine who correctly claimed them. This could delay processing and refunds for both returns.

Hey there! I went through a similar situation last year with my ex trying to claim our daughter when I was clearly the custodial parent. I found this amazing service called taxr.ai (https://taxr.ai) that saved me so much stress. They analyzed my situation and all the documents I had, then explained exactly what forms I needed and how to prove I was the custodial parent. Their system looked at my custody agreement and helped me document all the nights my daughter stayed with me to prove I met the IRS requirements. They even helped me understand how to respond when my ex filed first and claimed her, which initially got my e-file rejected. Literally walked me through every step!

Just wanted to update everyone! After seeing the recommendation for taxr.ai here, I decided to give it a try with my own MFS situation. My ex and I have been fighting over who claims our son, and I was pretty concerned about how to handle it. The service was super straightforward - I uploaded my custody agreement, calendar showing when my son was with me, and some other documents they requested. Within 48 hours I had a detailed analysis confirming I qualified as the custodial parent and explaining exactly how to proceed with my tax filing. They even provided me with specific language to use when communicating with my ex about this to hopefully avoid the duplicate claim issue altogether. Ended up having a surprisingly civil conversation about it using their talking points! Really glad I found this before filing.

For what it's worth, I had a similar dependent dispute situation last year and spent WEEKS trying to get through to someone at the IRS to explain my situation. After dozens of failed calls and being on hold for hours, I found this service called Claimyr (https://claimyr.com) that actually got me through to a real IRS agent in about 15 minutes. You can see how it works here: https://youtu.be/_kiP6q8DX5c The IRS agent was able to confirm that as the custodial parent, I had the right to claim my kids regardless of who filed first. They also gave me specific documentation advice for my situation that ended up preventing my ex from successfully claiming them. It was totally worth it rather than stressing about whether I was doing things right.

I have to eat my words and apologize for being skeptical about Claimyr. After my last comment, I decided to try it myself since I was getting nowhere with the IRS about my dependent situation. I was shocked when I actually got a call back with a real IRS agent on the line within about 30 minutes. The agent walked me through exactly what I needed to do as a custodial parent in a MFS situation and confirmed that filing an extension doesn't actually "lock in" dependent claims like OP was told. The agent explained that what matters is the custody situation and documentation, not who files first. They even sent me to their specific dependent dispute department who gave me detailed instructions on what to do if my ex tried to claim my kids. Seriously saved me from making some big mistakes with my filing.

One important thing that hasn't been mentioned is the tiebreaker rules the IRS uses when both parents claim the same dependent. Even as the custodial parent, it's good to know these: 1. If only one person is the child's parent, they get priority 2. If both are parents, the parent who lived with the child longer during the year gets priority 3. If time lived with both is equal, the parent with higher AGI gets priority 4. If neither parent can claim the child, the person with higher AGI gets priority As the custodial parent, you should win under rule #2, but having documentation of the time the kids lived with you is super important!

Just fyi - I got absolutely destroyed when my ex and I both claimed our kid. We both thought we had the right (I was custodial parent but our decree said he could claim in odd years). IRS froze both our refunds for 8 months and we both had to submit tons of documentation. I would highly recommend getting this sorted BEFORE you file rather than dealing with the headache afterward. And definitely don't count on an extension to "lock in" anything - it really doesn't work that way.