CP11
read it properlyMath Error on return — Balance Due
The IRS corrected something on your return and now says you owe money.
The notice states it verbatim: contact the IRS in writing within 60 days and it will reverse the change.
If it passes. You lose the automatic right to have the change reversed and the right to take it to Tax Court. The IRS says it will still look at late documentation, but the right is gone.
Why you got it
A math or clerical error assessment under IRC § 6213(b)(1).
What rights it carries
The abatement right in IRC § 6213(b)(2). On a timely written request the IRS SHALL abate — no documentation required. Once abated, normal deficiency procedures apply, which is how you get a Tax Court route.
Do you have to respond?
Optional if you agree. Use-it-or-lose-it in 60 days if you do not.
The mistake people make
Paying it. Paying an incorrect math-error assessment inside the 60 days gives up the cheapest reversal mechanism in the Code — a written request the IRS has to honour without proof.
If crypto is why this arrived, the number on it is probably wrong.
Your exchange reports what you sold for and leaves the cost box blank, so any figure the IRS computes from it treats every coin as though it cost you nothing. Rebuild the basis from your own transaction history — free — and see the real number before the deadline above runs out.
Notices that arrive around this one
CP3219A — The formal determination that you owe more tax — the ninety-day letter, and your one ticket to Tax Court without paying first. CP12 — The IRS corrected your return and you are owed a refund, or your refund amount changed. CP23 — You claimed more in estimated tax payments than the IRS has on record, and now you owe. CP14 — Your first bill. Tax has been assessed and it has not been paid.Every notice in the library → Not sure it is really from the IRS? →
Sources: IRS — Understanding your CP11 notice · CP11 specimen. Retrieved 2026-08-28. Where the IRS publishes no day count we say so rather than repeat a number we cannot source — the date printed on your own notice is the one that governs. ClearBasis is tax software, not a tax adviser, and this is information rather than advice.