Updated October 19, 2026. Quick answer: A CP11 means the IRS corrected one or more mistakes on your return and, as a result, the amount you owe has changed. Read what was changed, then either agree and pay by the date on the notice, or disagree and contact the IRS at the number shown by that date. The date matters: after it you lose formal reversal and Tax Court appeal rights.
Quick reference
| Item | As the IRS describes it |
|---|---|
| What it is | A return correction that changed the amount you owe |
| If you agree | Pay the amount owed by the date on the notice |
| If you disagree | Contact the IRS at the number on the notice by that date |
| Do not send | Your corrected copy of the return |
| Another correction | File Form 1040-X |
| Audit follow-up | Audit staff contact within 6 weeks if support is not received |
| Time to allow for an IRS reply (Tax Topic 651) | At least 30 days |
| Audit staff contact if support is not received | Within 6 weeks (42 days) |
| Amend later: generally within (Form 1040-X instructions) | 3 years of filing the original return, or 2 years of paying the tax, whichever is later |
What the notice says
“We corrected one or more mistakes on your tax return. As a result, the amount you owe has changed.”
To learn what was changed, “Review the “What we changed on your return” section of your notice.”
If you agree
The IRS says “Pay the amount owed by the date shown on your notice to avoid additional penalties and interest.” It also says to “Correct the copy of your tax return that you kept for your records, but do not send it to us.”
If you disagree
“Contact us at the number shown on the notice by the date indicated.” The IRS says “The fastest way to resolve many return errors is by telephone.”
“We’ll reverse most changes we made if we increased the amount you owe or if your return requested a refund.” You need not provide an explanation, though doing so may help.
The IRS warns that if you miss the date you “will lose formal rights to have the change(s) reversed, as well as your right to appeal our decision to the U.S. Tax Court.” If support for your original return is not received, the case may be forwarded for audit, and the audit staff will contact you within 6 weeks.
What you owe and from when
On interest, the IRS says “To avoid interest charges, full pay the amount owed by the due date shown on your notice.” It adds that, if not paid by then, “interest will accrue on the unpaid balance from the date the return was due.”
To make another correction later, “You’ll need to file a Form 1040-X, Amended U.S. Individual Income Tax Return”. See Form 1040-X.
If you need to correct the return yourself later
The Form 1040-X instructions give the time limit: “Generally, for a credit or refund, you must file Form 1040-X within 3 years (including extensions) after the date you filed your original return or within 2 years after the date you paid the tax, whichever is later.” See Form 1040-X for the form itself.
Where this comes from
The IRS page read for this page is the one titled Understanding your CP11 notice on irs.gov, as served on 2026-10-19. Your own notice controls: the dates, amounts and phone or fax numbers on it are the ones to use, and the IRS can update its page after we read it.
For IRS notices in general, Tax Topic 651 says “You should allow at least 30 days for a reply from the IRS.” It also says “Keep a copy of all IRS correspondence for your tax records.”
Common mistakes
- Letting the date on the notice pass while you decide whether to disagree. The IRS says formal reversal and Tax Court appeal rights are lost after it.
- Mailing a corrected copy of the return. The IRS says not to send it.
- Treating the notice as an audit. It corrects your return; an audit only follows if support is not received.
- Confusing CP11 with CP13 (zero balance) or CP12 (refund).
Related: the IRS math error notice, IRS Notice CP12, IRS Notice CP13, and IRS notices and letters.
Sources
- IRS, Understanding your CP11 notice (irs.gov): https://www.irs.gov/individuals/understanding-your-cp11-notice
- Instructions for Form 1040-X (Rev. December 2025), Amended U.S. Individual Income Tax Return: https://www.irs.gov/pub/irs-pdf/i1040x.pdf
- IRS, Tax Topic 651, Notices: what to do (irs.gov): https://www.irs.gov/taxtopics/tc651
Read from the IRS pages linked above on October 19, 2026. General information, not tax or legal advice. Your own notice and facts decide the outcome, and the number printed on your notice is the right place to confirm anything consequential.