You can’t file a traditional lawsuit against your ex for claiming your child on taxes, but you have two real remedies that do the same work. You can dispute the claim directly with the IRS, which will apply its own rules to decide who the rightful claimant is regardless of who filed first. And if a custody order addresses the tax claim, you can go to family court to enforce it, including asking the judge to hold your ex in contempt.
Which path matters more depends on your situation. The IRS route recovers the credits. The family court route punishes the violation and prevents the next one. Most people in this position end up using both.
Disputing the Claim With the IRS
Most parents find out about the problem when they try to e-file and the return bounces back. The IRS won’t accept an electronically filed return claiming a dependent whose Social Security number already appears on another return for the same year. The rejection doesn’t mean you’ve lost the claim. It means the e-file door is closed and you need to use the paper door.
File a paper return by mail claiming the child exactly as you would have electronically. Don’t attach extra documents trying to prove your case up front. If the IRS needs supporting documentation, it will contact both you and your ex by mail later.1Internal Revenue Service. Age Name SSN Rejects, Errors, Correction Procedures 4 The agency will then review both returns, apply its tiebreaker rules, and disallow the losing claim. The parent who loses has to pay back whatever credits they received, with interest.
Paper returns take significantly longer to process than e-filed ones, so expect your refund to be delayed while the duplicate claim is sorted out. If you need to go back and claim the child for a prior year, you generally have three years from the date you filed the original return or two years from when you paid the tax, whichever is later.2Internal Revenue Service. Time You Can Claim a Credit or Refund
How the IRS Decides Who Wins
The IRS uses its own tests to decide which parent claims the child, and those tests override whatever you and your ex agreed to informally. When two people claim the same child, the agency works through a tiebreaker sequence in order:
- If only one claimant is the child’s parent, the parent wins.
- Between two parents, the one the child lived with longer during the year wins.
- If the child lived with each parent the same amount of time, the parent with the higher adjusted gross income wins.
- If no parent claims the child, the non-parent with the highest AGI gets the claim.
These rules apply automatically. You don’t need to invoke them by name.3Internal Revenue Service. Tie-Breaker Rule You just need documentation that fits them.
The question of where the child actually lived is where most disputes turn. The IRS wants records from independent third parties showing the child lived at your address for more than half the year. School records, medical and pediatrician records, daycare billing statements, and letters on official letterhead from a school, doctor, or social service agency that list both your name and the child’s name at the same address with dates all qualify.4IRS.gov. Form 886-H-DEP Supporting Documents for Dependents Documents signed by a family member on your behalf won’t be accepted. Custody agreements and court orders can help, but they establish legal custody rather than physical residency, and the IRS cares most about where the child actually slept at night.
When a Divorce Decree Isn’t Enough
Here’s something that catches a lot of people off guard. The IRS does not consider itself bound by divorce decrees the way family courts do. For any divorce decree finalized after 2008, the IRS will not accept pages from the decree as a substitute for Form 8332, the form a custodial parent signs to release the dependency claim to the noncustodial parent.5Internal Revenue Service. Divorced and Separated Parents The noncustodial parent must have a signed Form 8332 or a substantially similar written statement to claim the child, no matter what the decree says.6Internal Revenue Service. About Form 8332, Release/Revocation of Release of Claim to Exemption for Child by Custodial Parent
If you’re the custodial parent and your ex claimed the child based only on a post-2008 decree without a signed Form 8332 from you, their claim is one the IRS won’t honor in a dispute. That’s a strong position going into the paper filing process.
For decrees finalized before 2009, the IRS may accept certain pages of the decree if it unconditionally grants the noncustodial parent the right to claim the child and the custodial parent signed it.
Taking It to Family Court
This is where the actual “suing” part of the question lives. You can’t file a civil damages lawsuit over a wrongful tax claim, but family court gives you real enforcement tools.
If your custody order specifies which parent claims the child and your ex violated it, you can file a motion asking the court to hold your ex in contempt. Contempt for willfully disobeying a court order can carry fines and, in serious cases, jail time. The court can also order your ex to amend their return to remove the improper claim, reimburse you for credits you lost, and pay the attorney’s fees you ran up bringing the motion.
If your custody order doesn’t mention tax claims at all, you can file a motion to modify the order and add specific language. Many family courts handle this with alternating-year arrangements, or by tying the claim to whichever parent had primary physical custody that year. Vague wording like “parents shall share tax benefits” invites the next fight. Specific terms stating which parent claims which child in which years prevent it.
One reality check on the family court side. Even when a judge orders your ex to amend their return, the IRS doesn’t enforce state court orders. Your ex has to comply voluntarily, and if they don’t, you’re back in court on another contempt motion. That’s why the faster move is usually to file your own paper return and let the IRS apply its tiebreaker rules while you pursue the family court angle for longer-term compliance.
What Your Ex Faces if the IRS Agrees With You
If the IRS determines your ex wrongfully claimed your child, the consequences escalate with how reckless or deliberate the claim looks.
When an underpayment results from negligence or disregard of the rules, the IRS imposes an accuracy-related penalty of 20% of the underpayment, on top of repaying the credits with interest. For gross valuation misstatements, that doubles to 40%.7Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
If the IRS finds that your ex claimed the Child Tax Credit or Earned Income Tax Credit through reckless or intentional disregard of the rules, it can ban them from claiming those credits for two years after the final determination. A fraud finding stretches the ban to ten years.8Internal Revenue Service. What To Do if We Deny Your Claim for a Credit After the ban ends, they have to file Form 8862 to reclaim eligibility.9Internal Revenue Service. Instructions for Form 8862 (12/2025)
In the most serious cases involving willful fraud, the IRS can refer the matter for criminal prosecution. Making false statements on a tax return is a felony punishable by fines up to $100,000 and up to three years in prison.10Office of the Law Revision Counsel. 26 USC 7206 – Fraud and False Statements Criminal prosecution for dependency disputes is rare, but it exists as an option when someone repeatedly and deliberately files false returns.
The money at stake is why these disputes get heated. For the 2025 tax year, the Child Tax Credit is worth up to $2,200 per qualifying child under 17.11Internal Revenue Service. Refundable Tax Credits The Earned Income Tax Credit reaches $8,231 for families with three or more children. Head of household status piles on a larger standard deduction and better brackets. A single wrongful claim can cost a parent well over ten thousand dollars.
Preventing It From Happening Again
The strongest preventive step is an Identity Protection PIN for your child. The IP PIN is a six-digit number that must appear on any return claiming that person. Without it, your ex’s return claiming the child will be rejected before it reaches the duplicate-claim stage. You can request an IP PIN for a dependent under 18 by submitting Form 15227 online or by visiting a Taxpayer Assistance Center in person with identity verification documents for yourself and the child.12Internal Revenue Service. Frequently Asked Questions About the Identity Protection Personal Identification Number (IP PIN)
Beyond the IP PIN, get the custody order amended so it names the claiming parent for each child in each year, and add a provision requiring cooperation with Form 8332 when the noncustodial parent is the designated claimant. Then file as early as you can each year. Filing first doesn’t guarantee you win an IRS dispute, but it means your return processes normally and your ex is the one dealing with the rejection and the paper delay.