When both parents claim the same child on their taxes, the IRS spots the duplicate Social Security Number and only one claim survives. The first return through the door goes through; the second gets rejected if e-filed, or triggers a review if mailed on paper. If neither parent backs down, the case goes to audit, and the IRS applies its own tie-breaker rules to decide who was entitled to the child. The losing parent repays the refund with 7% interest, may owe a 20% accuracy penalty (75% if the claim is judged fraudulent), and can be barred from claiming the affected credits for two or even ten years.
What the IRS Does When It Sees the Duplicate
Timing decides the first move. If one parent has already e-filed with the child’s SSN, the second parent’s electronic return will be rejected on the spot. The second parent then chooses: drop the child and refile electronically, or mail a paper return still claiming the child. Paper filing pushes both returns into the system, and the review begins.
Both parents then receive a Notice CP87A. It is not an audit. It says someone else claimed the same child and asks you to check whether your claim is correct. If the child isn’t really your dependent, the notice points you to Form 1040-X to amend. If you believe you are the rightful claimant, you do nothing.
When neither parent amends, the IRS escalates, usually with a CP75 notice. You have 30 days to send documentation proving the child lived with you. Miss that window and the IRS disallows the claim, then issues a notice of deficiency for the tax, penalties, and interest.
How the IRS Picks the Rightful Parent
Your custody order does not decide this. The IRS uses its own tie-breaker, and the first question is simple: which parent did the child live with for more nights during the tax year? That parent is the “custodial parent” for tax purposes and holds the default right to claim the child.
If the nights come out exactly equal, the tie goes to the parent with the higher adjusted gross income. Child support paid, who has legal custody under state law, and who covers more expenses do not enter the calculation.
Proof the IRS Wants to See
During an audit, your word isn’t the evidence. The IRS looks for third-party records tying the child’s address to your home during the year: school enrollment records, medical records, a lease or mortgage statement, childcare provider records, and government benefits paperwork. The more independent sources agree on the address, the stronger the claim.
Why the Divorce Decree Doesn’t Settle It
A state court order saying the noncustodial parent gets to claim the child carries no weight with the IRS on its own. To transfer the claim, the custodial parent has to sign Form 8332, and the noncustodial parent has to attach a copy to the return every year they claim the child.
Form 8332 is narrower than most parents assume. It releases the Child Tax Credit, Additional Child Tax Credit, and Credit for Other Dependents. It does not transfer the Earned Income Tax Credit or Head of Household status. Both of those stay with the custodial parent no matter what the form says. And if the custodial parent refuses to sign, the noncustodial parent cannot legally claim the child on a federal return; the remedy is back in family court, not with the IRS.
A release can also be revoked. A custodial parent who previously signed 8332 can complete Part III to revoke the release for future years, give a copy to the other parent, and file it with their own return. Past years already claimed stand; the transfer just stops going forward.
What the Losing Parent Owes
The parent whose claim gets disallowed has to pay back any refund they received on account of the child, plus tax they should have paid, plus interest running from the original filing deadline. The IRS charges 7% annually on underpayments, compounded daily. On a $3,000 underpayment sitting for a year, that’s roughly $210 in interest before any penalty.
On top of the interest, the IRS can add an accuracy-related penalty of 20% of the underpayment. If the agency concludes the claim was fraudulent rather than a mistake, the penalty rises to 75% of the underpayment attributable to fraud.
The dollars behind those percentages are real. The 2026 Child Tax Credit is worth up to $2,200 per child, with up to $1,700 refundable. The EITC for 2026 runs up to $4,427 with one qualifying child, $7,316 with two, and $8,231 with three or more, versus $664 for a worker with no children. Filing status can shift too: the 2026 standard deduction is $24,150 for Head of Household against $16,100 for Single, and losing the qualifying child can force the drop.
Two-Year and Ten-Year Credit Bans
Interest and a one-time penalty aren’t the ceiling. If the IRS concludes the claim was reckless or intentionally wrong, it can ban you from claiming the EITC, Child Tax Credit, and related credits for two years. If the claim is deemed fraudulent, the ban runs ten years. During the ban, you cannot claim those credits even if you have a legitimately qualifying child in a later year.
After a ban ends, or after any disallowance, you have to file Form 8862 with your next return that claims any of the affected credits. It re-certifies your eligibility, and the IRS will not release the credit without it.
Fixing an Incorrect Claim
If you now realize the child wasn’t yours to claim, file Form 1040-X to remove the dependent, adjust your filing status if it changes, and recalculate the tax. You can e-file 1040-X for the current year or the two prior years. Pay the balance quickly. Interest runs from the original due date of the return, not from when you file the amendment, so every month of delay adds to the bill. Installment agreements are available if you can’t pay in full, but interest keeps accruing until the balance is gone.
Preventing It Next Year
The clean prevention is a written agreement between parents about who claims the child in which year, paired with a signed Form 8332 for any year the noncustodial parent takes the claim. Get the form signed well before filing season, and keep the original.
If the concern is that the other parent will file first without permission, request an Identity Protection PIN for the child. An IP PIN is a six-digit number that has to appear on any return listing that SSN. Without it, a return claiming your child is rejected. Parents can request an IP PIN for a dependent under 18 by filing Form 15227 if AGI is below $84,000 for individual filers or $168,000 for joint filers, or by authenticating in person at an IRS Taxpayer Assistance Center. The PIN arrives by mail, and a new one is issued each year.