CP11: Changes to Your Return — Balance Due (Math Error Correction)

What it is

The mirror image of a CP12: the IRS says it 'corrected one or more mistakes on your tax return' and, as a result, 'the amount you owe has changed.' It is a correction-produced bill, not an audit — the notice shows what changed and the new amount due.

Why you got it

Sent when the IRS corrects what it believes is a mistake on a filed return and the correction results in a balance due.

The deadline structure

If you DISAGREE with the correction, contact the IRS at the number shown on the notice by the date indicated — the page states 'We'll reverse most changes we made if we increased the amount you owe or if your return requested a refund.' The math-error abatement right under IRC §6213(b)(2) generally gives you 60 days from the notice date to request that the assessment be abated; on a timely request the IRS must abate it and can only reassess by following formal deficiency procedures. If you AGREE, pay the amount owed by the date shown to avoid additional penalties and interest.

The current IRS CP11 page phrases every deadline as 'by the date shown on your notice' with no day count; the 60-day figure is the statutory math-error abatement window under IRC §6213(b), measured from when the notice is sent. Use the printed date as operative.

How to respond

• If you agree: pay the amount owed by the date shown on the notice; if you can't pay in full, the page says to make arrangements to pay over time
• If you disagree: call the toll-free number shown in the 'Where to find more information' section of the notice by the date indicated
• Supporting documents can be faxed using either a fax machine or an online fax service

What ignoring it leads to

Interest accrues on the unpaid balance from the date the return was due, and a late-payment penalty applies. If you don't contact the IRS by the date shown, the page says '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.'

Mistakes people make with a CP11

• Paying immediately without checking WHICH line changed — the correction can be wrong; verify the adjusted items against your own return and records before agreeing
• Missing that the dispute clock and the payment date are both printed dates — if you disagree, contact the IRS by the date shown or the formal reversal and Tax Court appeal rights are lost
• Assuming there's no option if you can't pay in full — the IRS page says to make arrangements to pay over time
• Skipping penalty relief — the page says to contact the IRS by the due date of the notice because it may be able to remove the penalty

Official sources

• Understanding your CP11 notice
• 26 U.S.C. §6213(b)(2) — abatement of math or clerical error assessments (60-day request; reassessment subject to deficiency procedures)

Our summary paraphrases these sources. Last verified: BUILD 2026-07-11 (Claude Fable 5; researched from live irs.gov fetches: https://www.irs.gov/individuals/understanding-your-cp11-notice, https://www.law.cornell.edu/uscode/text/26/6213 — CP11 page states 'by the date shown' with no day count; 60-day window is statutory §6213(b)(2), not printed) — re-verify before launch. Your printed notice always controls.

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