| Notice | Meaning |
|---|
| CP01A | Your Identity Protection PIN |
| CP05 | Refund on hold while return is verified |
| CP05A | Documents needed to verify your return |
| CP09 | You may qualify for the Earned Income Credit |
| CP11 | Math error — you now owe |
| CP12 | IRS corrected your return — refund changed |
| CP14 | Balance due — first notice |
| CP21A | Changes you requested — you owe |
| CP21B | Changes you requested — refund coming |
| CP21C | Changes you requested — no balance |
| CP22A | Changes made at your request — you owe |
| CP23 | Estimated payments didn't match — you owe |
| CP24 | Estimated payments didn't match — refund |
| CP27 | You may qualify for the Earned Income Credit (no children) |
| CP30 | Estimated tax penalty charged |
| CP30A | Estimated tax penalty adjusted |
| CP32A | Call to get your refund reissued |
| CP45 | Overpayment couldn't go to next year |
| CP49 | Refund applied to a tax debt |
| CP53 | Direct deposit failed — paper check |
| CP53E | Direct deposit failed — add bank account in 30 days |
| CP59 | No tax return filed |
| CP60 | Payment removed — balance due |
| CP63 | Refund held — missing return |
| CP71 | Annual reminder of balance due |
| CP71A | Annual reminder of balance due |
| CP71C | Annual reminder — passport may be denied |
| CP75 | Audit — refund held, documents needed |
| CP81 | Return not filed — refund at risk |
| CP87A | Dependent or SSN claimed on another return |
| CP90 | Final notice — intent to levy |
| CP92 | State refund levied — right to a hearing |
| CP134B | Federal tax deposits don't match — balance due |
| CP161 | Business balance due |
| CP210 | IRS changed your business return |
| CP215 | Civil penalty charged |
| CP220 | IRS changed your business return |
| CP261 | S corporation election accepted |
| CP297 | Intent to levy federal payments |
| CP501 | Reminder — you still have a balance |
| CP503 | Second reminder — balance still unpaid |
| CP504 | Notice of intent to levy |
| CP504B | Business notice of intent to levy |
| CP508C | Passport certification — seriously delinquent debt |
| CP518 | Final reminder — return not filed |
| CP521 | Installment agreement payment reminder |
| CP523 | Payment plan in default |
| CP575 | Your new EIN |
| CP2000 | Proposed changes — income doesn't match |
| CP2100 | Backup withholding notice (50+ mismatches) |
| CP2100A | Backup withholding notice (under 50 mismatches) |
| CP2501 | Income mismatch — explain the difference |
| CP3219A | Notice of deficiency (90-day letter) |
| LT11 | Final notice of intent to levy |
| LT16 | Overdue taxes or missing returns |
| LT39 | Reminder — overdue balance or returns |