CP11· Math-error correction
CP11 — Math-error correction with balance due
- Category
- Math error
- Urgency
- Date on notice
- Response window
- see notice
- Key form
- Form 1040-X
Respond by the date printed on your individual notice.
Why the IRS sent this
IRS-detected math / processing error on your filed return that increased the tax.
Response window
The IRS detail page for CP11 does not state a fixed day count. The response-by date is printed on your individual notice — read the date at the top-right corner.
For statutory windows referenced by the IRS detail page, see the cited Publication for procedural timing.
What to do
Required action
Review the corrections; pay the new balance by the date on the notice, or contact the IRS by that date if you disagree.
Key form: Form 1040-X — verify the current revision on irs.gov/forms-pubs before filing.
Appeal path
Informal — call the IRS
Informal dispute by calling the IRS at the toll-free number on the notice. The U.S. Tax Court is referenced for formal appeal rights, exercisable before the deadline.
Notes from the primary source
IRC §6213(b) provides a statutory 60-day window to request abatement of math-error adjustments. The IRS detail page does NOT restate this window — verify with Publication 1 or the statute directly before relying on the 60-day count.
Calm-corrective
Only the IRS can resolve your notice
We are not a CPA firm, not a law firm, not an Enrolled Agent firm, and not affiliated with the IRS. We don't accept payments on your behalf, settle your debt, or call the IRS for you. What we do: explain what your notice means, point you to the right IRS form, cite the statute that authorizes the action, and surface the appeal path. Then you call the number on the notice, file the form, or hire a licensed professional.
Related notices
Likely next or sibling codes
Source
Verified against the official IRS detail page on irs.gov/individuals/understanding-your-cp11-notice. Always re-verify against the IRS page before acting.