What Is IRS Notice CP11?

A CP11 notice means the IRS reviewed your tax return, identified what they believe is a math error or miscalculation, corrected it, and is now billing you for the additional tax that results from the correction. The IRS has broad authority to correct mathematical errors without your permission, so by the time you receive a CP11, the change has already been applied to your account.

The notice will explain exactly what was changed: for example, a credit you claimed was calculated incorrectly, a number from one part of the return doesn't carry over correctly to another, or an income amount doesn't match a form the IRS has on file. It will show the original amounts, the corrected amounts, and the resulting balance due (plus any penalties and interest if applicable).

If you agree with the correction, simply pay the amount due. If you disagree — for example, if you believe the IRS made an error in their "correction" or you have documentation supporting your original calculation — you have 60 days from the date of the notice to dispute it. Send a written response by mail explaining your position and including any supporting documentation. Unlike a CP2000, which is a proposal you can formally accept or reject, the CP11 reflects a change that has already been made to your account — so if you disagree, you're asking the IRS to reverse a change they've already applied.

If you don't pay or dispute the CP11 within the response period, the balance due becomes subject to normal IRS collection action — the same sequence of reminder notices and potential levy that applies to any unpaid tax balance. Math error notices are relatively common and are often the result of simple calculation errors on the return rather than intentional misreporting, so they typically don't lead to further audit activity. If the error resulted from a tax software glitch or a misunderstanding of a complex rule, it may be worth having a tax professional review your situation before responding.