Bills for tax you owe
CP14Balance due noticeA CP14 is an IRS bill saying you owe money on unpaid taxes, with the amount due and how to pay it.
CP501Balance due reminderA CP501 is a follow-up reminder that you still have unpaid tax on one of your accounts and the IRS hasn't received a payment or reply.
CP503Second balance due reminderA CP503 is the IRS's second reminder about tax you still owe on one of your accounts, sent because it hasn't heard from you.
Final notices and levies
CP504Notice of intent to levyA CP504 is a notice of intent to levy, sent because your tax balance is still unpaid, and it asks you to pay the amount due right away.
LT11Final intent to levy noticeAn LT11 or Letter 1058 says the IRS plans to levy (seize) your property for overdue taxes and explains your right to a hearing.
CP90Levy and hearing rights noticeA CP90 says the IRS intends to levy certain assets to pay unpaid taxes and tells you about your right to a Collection Due Process hearing.
The IRS changed your return
CP30Estimated tax penalty noticeA CP30 says the IRS added a penalty because you didn't prepay enough tax during the year through withholding or on-time estimated payments.
CP11Return changed, balance dueA CP11 says the IRS fixed one or more errors on your tax return, and the fixes changed how much you owe.
CP12Return changed, refund adjustedA CP12 says the IRS fixed one or more errors on your tax return, so you're now due a refund or your refund amount changed.
Income mismatches and proposed changes
CP2000Proposed changes to your returnA CP2000 proposes changes to your tax return because income or payment information from employers, banks or others doesn't match what you reported.
CP2501Income mismatch inquiryA CP2501 asks you to respond because income or payment information the IRS got from third parties doesn't match your tax return.
CP3219AStatutory notice of deficiencyA CP3219A is a statutory notice of deficiency that proposes a change to your tax based on information from others and explains your U.S. Tax Court rights.
Payment plans
CP523Payment plan default noticeA CP523 says you've defaulted on your installment agreement and the IRS intends to end the agreement and levy your assets.
CP521Payment plan reminderA CP521 reminds you that a monthly payment on your installment agreement is due and asks you to send it right away.
Missing returns
Business notices
CP161Business balance due noticeA CP161 says you have an unpaid balance due on a tax account, explains how the IRS figured it, and asks you to pay by the date shown.
CP162Partnership or S corp penaltyA CP162 says the IRS charged your partnership or S corporation a penalty, such as for a late or incomplete return or not filing electronically when required.
972CGProposed information return penaltyNotice 972CG proposes a penalty for information returns, like Forms W-2 and 1099, that were filed late, not e-filed when required, or had missing or incorrect taxpayer ID numbers.
Don't see your notice? The IRS lists every notice and letter on its Understanding your IRS notice or letter page. Whatever the notice says, check the deadline printed on it first.