A CP21A arrives after the IRS has processed a change to your tax return — whether from an amended return you filed, an IRS correction, or an adjustment following a previous notice — and that change resulted in additional tax being owed.
Unlike the CP11, which reflects an automated math correction, the CP21A typically follows a more deliberate change — one that either you initiated or the IRS made based on a prior audit or notice response.
What the CP21A means
The CP21A confirms that a specific change was made to your return and that, as a result, a balance is now due. The notice identifies the tax year, the nature of the change, and the amount owed including any penalties and interest already accrued.
The balance shown is assessed — not proposed. Interest continues accruing daily until it’s paid.
What to do
Verify that the change described matches what you expected. If you filed an amended return, confirm that the balance reflects the changes you submitted. If the IRS made the change based on a prior correspondence, compare it against what was agreed or proposed at that stage.
If you agree, pay the balance or establish a payment plan before the deadline — typically 21 days. If you believe the change is incorrect, respond in writing within 60 days with documentation explaining the discrepancy.
Frequently asked questions
What triggers a CP21A? Usually an amended return you filed, or a change the IRS made based on a prior audit, notice response, or compliance review.
Is the balance on a CP21A negotiable? The underlying tax generally isn’t, but penalties may be eligible for abatement if you qualify for First-Time Penalty Abatement or have reasonable cause.