Updated October 19, 2026. Quick answer: A CP12 means the IRS corrected one or more mistakes on your return and, as a result, you are now due a refund or your original refund amount changed. If you agree, no response is required and a refund check should arrive in 4 to 6 weeks. If you disagree, contact the IRS at the number on the notice by the date shown.
Quick reference
| Item | As the IRS describes it |
|---|---|
| What it is | Math or return-error correction that creates a refund or changes the refund |
| If you agree | No response required |
| If you disagree | Contact the IRS by the date on the notice |
| Time to allow for an IRS reply (Tax Topic 651) | At least 30 days |
| Refund check | 4 to 6 weeks (28 to 42 days) |
| Audit staff contact if support is not received | Within 6 weeks (42 days) |
| Refund after a notice, if you owe nothing else the IRS must collect (Tax Topic 651) | Within 6 weeks of the notice date, which is 42 days |
What the notice says
“We corrected one or more mistakes on your tax return. As a result, you are now either due a refund or your original refund amount has changed.”
The IRS says it issues a CP12 when it corrects errors and “The refund is different from the one you expected” or “You have a refund when you thought you owed money or had an even balance.”
What you need to do
“If you agree with the changes we made, no response is required.” The IRS adds that a refund check should arrive in 4 to 6 weeks as long as you do not owe other tax or debts it is required to collect.
To see what changed, “Review the “What we changed on your return” section of your notice.” You may want to correct the copy of the return you kept, but the IRS says not to send it in.
If you disagree
“If you disagree, contact us by the date shown on your notice.” The IRS says “The fastest way to resolve many return errors is by telephone.”
On reversals: “We’ll reverse most changes we made if we reduced the refund you requested on your return.” You do not have to explain, though “doing so may help us resolve your case more quickly.”
The IRS warns: “If you don’t contact us by the date shown on your notice, 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.” Support sent later is still considered.
If the IRS cannot confirm your original return
The IRS says “we may forward your case for audit, in which case the audit staff will contact you within 6 weeks to explain the process and your rights.” For the general picture of math-error notices see the IRS math error notice.
Where this comes from
The IRS page read for this page is the one titled Understanding your CP12 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.” On refunds it says “you’ll receive the refund within 6 weeks of the notice date.”
Common mistakes
- Calling after the date on the notice. The IRS says formal reversal rights and Tax Court appeal rights are lost after that date.
- Mailing a corrected return. The IRS says not to send your corrected copy; it is for your records.
- Assuming the new refund is wrong because it differs from your return. Read what the IRS changed first.
- Confusing CP12 with CP11 or CP13. CP12 creates or changes a refund; CP11 changes an amount owed; CP13 leaves a zero balance.
Related: the IRS math error notice, IRS Notice CP13, IRS Notice CP11, and IRS notices and letters.
Sources
- IRS, Understanding your CP12 notice (irs.gov): https://www.irs.gov/individuals/understanding-your-cp12-notice
- 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.