IRS Reference Number 9024 is a math error code indicating that the IRS adjusted your return and assessed a balance due, almost always because Form 8962 was missing or incomplete and the agency removed your Advance Premium Tax Credit. The label “math error” is misleading. Nothing was miscalculated in the arithmetic sense. The IRS’s system detected a gap between your return and third-party data from the Marketplace, stripped the credit out, and billed you for the difference. You have 60 days from the date on the notice to respond, and that deadline controls almost everything about what happens next.
What Triggers the 9024 Code
If you had Marketplace health coverage and received advance subsidies to lower your monthly premiums, you’re required to file Form 8962 with your return to reconcile those advance payments against the credit you actually qualify for.1Internal Revenue Service. Instructions for Form 8962 (2025) When that form is missing, the IRS doesn’t pause and ask for it. Its system removes the entire advance credit from your tax calculation, creating an immediate balance due, and classifies the adjustment as a math error under code 9024.
This distinction matters: a 9024 notice is a math error notice, not a CP2000 underreporter notice. Under 26 USC 6213(b), the math error authority lets the IRS assess additional tax right away without first sending a proposal and waiting for your reply.2Office of the Law Revision Counsel. 26 USC 6213 – Restrictions Applicable to Deficiencies; Petition to Tax Court The assessment is already on the books when the notice arrives. Your job is to unwind it.
The 60-Day Deadline That Controls Everything
You have 60 days from the mailing date of the notice to request abatement of the math error assessment. The request can be written or oral, but writing it down creates the record you’ll want if anything goes wrong. If you make the request in time, the IRS must reverse the assessment. The Internal Revenue Manual states the IRS “shall abate” upon a timely request.3Internal Revenue Service. Internal Revenue Manual 21.5.4 – General Math Error Procedures During those 60 days, the IRS also cannot levy your bank accounts or wages for the assessed amount.
Miss the window and the assessment becomes final. You lose the right to petition the U.S. Tax Court before paying. Your only option then is to pay the tax, file a refund claim, and, if it’s denied, sue in federal district court or the Court of Federal Claims.4Taxpayer Advocate Service. 2023 Purple Book – Allow Additional Time for Taxpayers to Request Abatement of a Math Error Assessment That path is slower and more expensive than responding on time.
If you request abatement in time and the IRS still believes you owe the tax, the agency has to switch tracks and follow normal deficiency procedures. That means a formal notice of deficiency (the 90-day letter), which gives you the right to petition the Tax Court before paying anything.
How to Fix It
For most 9024 notices, the fastest fix is not fighting the assessment but supplying the missing form. Filing Form 8962 lets you calculate the credit you were actually entitled to and usually reduces the balance sharply, sometimes to zero or to a refund.
- Find your Form 1095-A. Check your Marketplace account, or call the Marketplace at 1-800-318-2596 if you never received it. Check that the figures are correct, especially the second lowest cost Silver plan amounts in Column B.5HealthCare.gov. How to Use Form 1095-A Health Insurance Marketplace Statement
- Complete Form 8962 using the 1095-A data and your actual household income. The form calculates the credit you qualify for and compares it to the advance payments made on your behalf.6Internal Revenue Service. About Form 8962, Premium Tax Credit
- Send the completed Form 8962, a copy of your 1095-A, and any supporting income documentation to the address or fax number printed on your notice. Do not use the regular IRS filing address.
- Request abatement in writing within 60 days if you need more time to gather documents or you disagree with the adjustment. That forces the IRS to reverse the assessment and follow normal procedures.
- Keep copies of the notice, the forms you send, and any fax confirmation or certified mail receipt.
What It Costs If You Wait
Once a math error assessment is in place and unpaid, the failure-to-pay penalty runs at 0.5% of the unpaid tax per month or partial month, capped at 25%. The rate drops to 0.25% per month if you’re on an approved payment plan.7Internal Revenue Service. Failure to Pay Penalty
Interest compounds daily on top of the penalty. For the quarter beginning April 1, 2026, the individual underpayment rate is 6%, set as the federal short-term rate plus three percentage points, and it adjusts quarterly.8Internal Revenue Service. Internal Revenue Bulletin 2026-08 Interest runs from the original due date of the return, not from the date of the notice, so a balance from an April-due return has already been accruing interest by the time you open the envelope.
The stakes are higher for 2026 than in earlier years. Under Pub. L. 119-21, the repayment caps that used to limit how much excess advance credit lower-income households had to pay back were removed for tax years beginning after December 31, 2025.9Office of the Law Revision Counsel. 26 USC 36B – Refundable Credit for Coverage Under a Qualified Health Plan Starting with 2026 returns, you repay the full difference between advance payments and your actual credit regardless of income.10Internal Revenue Service. Updates to Questions and Answers about the Premium Tax Credit That change matters twice: it raises the excess repayment you might legitimately owe, and it makes the IRS’s “assume the whole advance is excess” default calculation much more painful when Form 8962 is missing. Filing the form is the only way to establish that you were entitled to any credit at all.
The Effect on Your Marketplace Subsidies
Leaving a 9024 notice unanswered creates a second problem beyond the tax bill. If you don’t file Form 8962 to reconcile prior-year advance credits, the Marketplace can flag your account as Failure to Reconcile and stop advance credit payments on your current or future coverage, forcing you to pay the full unsubsidized premium each month until the flag clears.11Internal Revenue Service. Premium Tax Credit – Claiming the Credit and Reconciling Advance Credit Payments
Clearing it takes the same step that resolves the tax notice: file the missing Form 8962. You have to file a return for any year in which you received advance credits, even if your income was otherwise below the filing threshold. Once the IRS processes the return with Form 8962 attached, reconciliation is complete and Marketplace eligibility for advance payments should be restored.