CP21A

A CP21A says the IRS made changes to your return — typically following a correction or adjustment request — and the result is a balance due. It states what changed and bills the difference.

“The changes are made, and they result in an amount owed. Pay by the date printed on the notice, or use a payment plan, temporary collection delay, or offer in compromise if you can't. Disagree? Call the number on the notice with your return and the notice in hand.”

Paying by the printed date stops further interest; missing it adds a late-payment penalty, which the IRS itself notes can sometimes be removed if circumstances beyond your control caused the delay and you contact them by the due date.

• The notice and your return for that year
• The adjustment request or amended return that triggered the change, if you made one
• Payment records
• Notes on anything about the change that doesn't match what you requested

• Verifying the change matches what was actually requested — adjustments sometimes land wrong
• Contesting a change you never asked for, which can signal an account mix-up or identity issue
• Arranging payment terms when the balance is real
• Pursuing penalty relief by the due date