IRS Notices Explained: Every Major Letter Decoded

The IRS sends hundreds of different notices. This hub covers the 20 most common ones in plain language. Type your notice code in the search box below to jump straight to it.

The IRS sends over 200 million notices each year. Most are routine, but some demand immediate action. This guide covers the 20 most common notices — what each means, the urgency level, and what to do. Use the search box below to filter by notice code (e.g. "CP504") or keyword (e.g. "levy", "lien").

Urgency levels explained

Critical — immediate action required, often with a 30-day deadline. Ignoring leads to levy or seizure.
High — action required within weeks; collection consequences approach if ignored.
Medium — response needed but not time-critical.
Low / Informational — routine; no urgent action required.

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Showing 20 of 20 notices

Collection notices (14)

Notice	What it means	Urgency
CP14	First balance due notice	Medium
CP501	Reminder of balance due	Medium
CP502	Second reminder of balance	Medium
CP503	Second reminder — immediate action needed	High
CP504	Final notice of intent to levy state tax refund	High
CP504B	Final notice for business balances	High
CP521	Installment agreement reminder	Low
CP523	Installment agreement default warning	High
CP71C	Annual reminder of balance	Low
CP90	Final Notice of Intent to Levy (CDP rights)	Critical
LT11	Final Notice of Intent to Levy	Critical
Letter 1058	Final Notice of Intent to Levy (Revenue Officer)	Critical
Letter 3172	Notice of Federal Tax Lien filed	High
Letter 668-D	Lien or levy release notification	Informational

Examination notices (4)

Notice	What it means	Urgency
CP2000	Proposed changes to return (automated matching)	High
CP2501	Request for additional information	Medium
CP22A	Account adjustment — balance due	Medium
CP3219A	Notice of Deficiency (90-day letter)	Critical

Non-Filing & Levy notices (2)

Notice	What it means	Urgency
CP2566	Substitute for Return proposed assessment	High
Letter 11	Final Notice of Intent to Levy	Critical

What to do when you get an IRS notice

Do not ignore it. Every notice has a deadline.
Read it carefully. Identify the notice code (top-right corner), tax year, amount, and deadline.
Look up the specific notice on this page to understand what it means.
Determine if you agree. The IRS is sometimes wrong.
Respond by the deadline. Even if you disagree — silence is worse than contesting.