If your ex claims your child on their taxes and you also claim that child, the IRS flags both returns and starts a process to figure out which parent was entitled to the dependent. The parent the child actually lived with for more than half the year almost always wins. While that gets sorted out, refunds can be held, and the parent who filed the improper claim ends up repaying any tax benefits received, with interest, and often a penalty of 20% to 75% of the resulting underpayment.
What the IRS Does When Two Returns Claim the Same Child
The IRS system matches dependents by Social Security number. When two returns claim the same child, the first one filed electronically is accepted. The second e-filed return is rejected with an error saying the dependent has already been claimed. The second filer then has to mail a paper return, which can push the refund back by months.
Starting with 2024 returns filed in 2025, there is one exception. If the second filer has a valid Identity Protection PIN (IP PIN) for themselves and includes it on the return, the IRS will accept the second e-filed return.1Taxpayer Advocate Service. Protect Yourself From Tax-Related Identity Theft – Get an Identity Protection PIN Accepting both returns is not the IRS deciding anything on the merits. It just keeps the second filer out of paper purgatory while the dispute moves forward.
Once both returns are in, the IRS mails each filer a CP87A notice. The notice says someone else claimed the same dependent and asks you to review the rules. It does not tell you who the other filer was.2Internal Revenue Service. Understanding Your CP87A Notice If neither parent amends to back down, the IRS can open an audit to decide who was entitled.
The CP87A itself is not an audit. It is informational. If you are confident the child qualifies as your dependent, you do not need to send documents at that stage.3Internal Revenue Service. Notice CP87A – You Need to Make Sure Someone Is Your Dependent If you realize you should not have claimed the child, you file an amended return on Form 1040-X.
Who the IRS Says Actually Gets to Claim the Child
The IRS does not care what your custody order says about taxes. It cares about where the child slept at night. The parent the child lived with for the greater number of nights during the tax year is the custodial parent for tax purposes, and that parent has the default right to claim the child.4Internal Revenue Service. Claiming a Child as a Dependent When Parents Are Divorced, Separated or Live Apart For a full calendar year, that means at least 183 nights. If the nights were split exactly evenly, the tiebreaker goes to the parent with the higher adjusted gross income.
Nights your child was temporarily away from your home still count as nights with you. School, summer camp, a hospital stay, a vacation — all are treated as temporary absences from the child’s regular residence.5Internal Revenue Service. Qualifying Child Rules
This is where most of these disputes start. A divorce decree saying “Dad claims the child in even years” is not enough for the IRS. For any decree or separation agreement that took effect after 2008, the non-custodial parent cannot substitute pages from the decree for the required IRS release.6Internal Revenue Service. Form 8332 – Release/Revocation of Release of Claim to Exemption for Child by Custodial Parent The only way a non-custodial parent can legally claim the child is if the custodial parent signs Form 8332 releasing the claim and the non-custodial parent attaches it to their return every year they use it. Without that signed form, the IRS sides with the custodial parent regardless of what a judge ordered.
What to Do Right Now If Your Ex Already Claimed Your Child
If your e-filed return was rejected because the child’s SSN was already used, and you are the custodial parent, you still file. You print the return and mail it in. Expect the IRS to send a CP87A to both of you and, eventually, to ask one or both parents to prove the child lived with them.
Going forward, get an IP PIN. An IP PIN is a six-digit number the IRS assigns to your account that has to appear on your return. It is the single most effective preventive step for a parent worried the other parent will file first again next year, because it lets you e-file even if someone else has already claimed your child.
Anyone with a Social Security number or ITIN can request an IP PIN through their IRS online account, and parents can request IP PINs for their dependents. If you cannot verify your identity online, you can file Form 15227 (if your AGI is below $84,000 for single filers or $168,000 for joint filers) or visit a Taxpayer Assistance Center in person.7Internal Revenue Service. Get an Identity Protection PIN Dependents under 18 have to use one of the alternative methods rather than the online tool.
If your ex improperly claimed your child in a prior year and you missed credits you were entitled to, you can file an amended return on Form 1040-X. You can e-file an amended return for the current year or the two prior years.8Internal Revenue Service. Instructions for Form 1040-X (Rev. December 2025) There is a hard deadline: you must file within three years of the date you filed the original return, or two years from the date you paid the tax, whichever is later.9Internal Revenue Service. Time You Can Claim a Credit or Refund
What You Keep as the Custodial Parent Either Way
Even when a custodial parent signs Form 8332, only three benefits transfer to the other parent: the child tax credit, the additional child tax credit, and the credit for other dependents.4Internal Revenue Service. Claiming a Child as a Dependent When Parents Are Divorced, Separated or Live Apart Several more valuable benefits stay with the custodial parent and cannot be transferred:
- The Earned Income Tax Credit, which requires the child to live in the same home as you for more than half the year. Form 8332 has no effect on EITC.5Internal Revenue Service. Qualifying Child Rules
- The dependent care credit, for childcare expenses that let you work.
- Head of household filing status, which also requires the child to have lived with you for more than half the year.
If you are the custodial parent, claim EITC, the dependent care credit, and head of household status even in years when the other parent properly claims the child tax credit. Releasing the dependency claim does not release these.
If the IRS Asks for Proof
When the dispute escalates past the CP87A stage, the IRS sends a different notice, often a CP75, that asks for specific documentation and gives you a deadline, typically 30 days, to respond.10Internal Revenue Service. Notice CP75 Send your response by a method that gives you delivery confirmation.11Internal Revenue Service. IRS Audits
What the IRS wants is records showing your child’s address matched yours for more than half the year. School records are the most commonly used proof, but the copies must include your name and the child’s address, and the dates have to cover more than half the tax year. A single semester may not be enough on its own.12Internal Revenue Service. Topic No. 654 – Understanding Your CP75 or CP75A Notice, Request for Supporting Documentation Medical or dental records showing the child’s home address, daycare statements, social service records, and a lease or utility bills in your name at the child’s address all help.
If you are the non-custodial parent claiming the child with a signed Form 8332, that form is your primary evidence. Keep the original and attach a copy to your return.
What the Parent Who Loses Faces
The parent who loses has to repay whatever tax benefit they received from claiming the child, with interest running from the original due date of the return. On top of repayment, the IRS can impose an accuracy-related penalty of 20% of the underpayment where the improper claim came from negligence or disregard of the rules.13Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments If claiming the child cut your ex’s tax by $2,000 and the claim was improper, that is $400 in penalty on top of the $2,000 and interest.
If the IRS determines the claim was fraudulent rather than careless, the penalty is 75% of the underpayment.14Office of the Law Revision Counsel. 26 USC 6663 – Imposition of Fraud Penalty On that same $2,000, the fraud penalty would be $1,500. Once a dependent claim is flagged, the IRS can audit the rest of the return as well.
If the child was also used to claim the EITC, the consequences get steeper. The IRS can ban a taxpayer from claiming the EITC for two years if the claim was due to reckless or intentional disregard of the rules, or for ten years if the claim was fraudulent. Those bans apply to all future EITC claims, not just the child in question.
The 20% accuracy-related penalty can be waived if you can show reasonable cause and good faith. The IRS weighs what you did to determine the correct treatment, the complexity of the issue, and whether you relied on a qualified tax professional who had all the facts.15Internal Revenue Service. Penalty Relief for Reasonable Cause A parent who genuinely believed they were the custodial parent under a confusing custody arrangement has a stronger case than one who ignored the rules. Reasonable cause does not apply to the 75% fraud penalty.