IRS CP11 Notice: Math Error — Balance Due
A CP11 notice means the IRS corrected what it considers a miscalculation on your return and the change results in a balance due — you have 60 days to dispute it before the assessment becomes final.
Deadline calculator
The CP11 clock runs from the date printed on the notice — not the day you opened it.
Estimate only, based on the standard 60-day CP11 window. Your notice controls — always use the specific date printed on it.
What a CP11 actually means
"Math error" is broader than arithmetic: mismatched credits (Child Tax Credit, stimulus/recovery amounts), wrong SSNs for dependents, and income transcription errors all trigger CP11s.
The 60-day window matters: request abatement within it and the IRS must reverse the change and follow normal deficiency procedures (with full appeal rights) if you disagree. Miss it, and you owe the tax unless you pay and claim a refund later.
How to recognize a real CP11
An IRS campus sends it when a math or clerical correction during processing turns the return into a balance due. The IRS can make this kind of change without an audit, which is why the notice comes with a reversal right.
- The heading reads 'Changes to your [year] Form 1040' with 'Amount due:' in large type and a bulleted list of the areas affected, such as the Child Tax Credit or Earned Income Tax Credit.
- A Billing Summary shows tax owed, payments made, any failure-to-file penalty, interest, and a due date. A detachable payment stub is at the bottom of page 1.
- A 'Changes to your [year] tax return' section gives the reason in plain words, such as a child exceeding the age limit for the Child Tax Credit.
- A 'Your tax calculations' table shows 'Your calculation' next to 'IRS calculation'.
- It says you can get the change reversed by contacting the IRS in writing within 60 days, without having to provide an explanation.
What to do, step by step
- 1Compare the notice's 'changes to your return' section against your filed copy line by line.
- 2If the IRS is right, pay or set up a payment plan — interest runs from the return due date.
- 3If you disagree, call or write within 60 days and request abatement of the math-error assessment.
- 4Provide documentation supporting your original figures (credit eligibility, dependent SSNs, etc.).
Illustrative example
Example: Marisol's Child Tax Credit is disallowed over a birthdate
Marisol (an illustrative taxpayer) claimed the Child Tax Credit for her son on her 2025 return. A CP11 dated June 8, 2026 said one or more children exceeded the age limit, removed the credit, and showed $1,140 due by the date on the notice.
Her son actually met the age rule. The IRS records had the wrong birthdate because of a typo on the return. On June 20 she wrote to the address on the notice asking for the change to be reversed, and enclosed a copy of his birth certificate. The written request was well inside the 60-day window, which ran to August 7, 2026.
A timely written request means the IRS reverses the change. If the IRS still thought the credit was wrong, it could send the case to audit, and Marisol would keep formal appeal rights, including Tax Court, before having to pay. If she had agreed with the change, the right move would have been to pay by the due date, since interest and penalties keep growing on what's unpaid.
Names and numbers are made up to show how this notice typically plays out.
Mistakes that make a CP11 worse
- Disputing by phone only. The 60-day reversal right applies to written contact. The notice says a call is for questions about the amount due.
- Waiting to gather perfect documentation before responding. The notice says you don't have to explain or send documents to request the reversal. A timely written request is what protects your rights, and you can send support with it.
- Paying and then disputing. After 60 days, or once you've effectively accepted the change, your only remedy is a refund claim, generally within 3 years of filing or 2 years of payment, whichever is later.
- Sending a corrected return to the IRS when you agree. The IRS says to fix your own copy and pay, not to resubmit the return.
What happens if you ignore a CP11
The IRS assumes you agree. After 60 days it won't reverse the change, and you lose the right to appeal before paying. The balance keeps growing with interest and late-payment penalties, and unpaid amounts move into the regular balance-due reminder notices.
Can come next
Common questions
Why does my CP11 say my Child Tax Credit was wrong?+
Credit-eligibility mismatches (age, SSN validity, income phase-outs) are the most common CP11 trigger. If your records show the credit was right, dispute within 60 days — after that, reversal requires a refund claim.
Checked against IRS primary sources — see how we source these guides. You can verify any notice directly at IRS.gov. The dates and instructions printed on your specific notice always control. Official IRS explanation: Understanding your CP11 notice.
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