Or search by code (CP2000, CP14, LT11, Letter 226-J) or keyword (audit, levy, underreporter, refund hold, identity verification, penalty).
Every IRS notice carries an identifying number in the upper-right corner — a “CP” number for computer-generated notices (for example, CP14 or CP2000) or an “LTR”/“Letter” number for correspondence (for example, 5071C). That code, not the wording, tells you exactly what the notice is and what response it expects. The notice also states the tax year, the amount at issue, the action required, and a response deadline. Reading those four pieces first prevents most missteps.
Notices generally fall into a few families: math-error corrections, balance-due bills, the underreporter (information-matching) program, identity-verification requests, and collection actions. This tool maps the most common notice numbers to what they mean, how urgent they are, and how to respond, so you can triage quickly.
Math-error and adjustment notices (such as CP11, which shows a balance due after a correction, or CP12, which shows a changed refund) report that the IRS altered a figure on your return. Balance-due notices escalate: CP14 is the first bill, CP501 and CP503 are reminders, and CP504 is a notice of intent to levy a state refund. CP2000 is an underreporter notice proposing changes because the income reported to the IRS on W-2s and 1099s does not match your return — it is a proposal, not a bill, and you can agree or dispute it. Identity-verification letters (5071C, 4883C, 5747C) hold your refund until you confirm you filed the return. Final collection notices such as LT11 or Letter 1058 precede a levy and carry important appeal rights.
The most damaging mistake is ignoring a notice or missing its deadline — many notices preserve appeal or response rights only if you act in time, even when you disagree. A CP2000 is not a final assessment; responding with documentation can reduce or eliminate the proposed change. Always keep a copy of the notice and your response, and send disputes by a method that provides proof of mailing. If a notice claims you filed a return you did not file, treat it as possible identity theft and respond through the verification channel the letter specifies.
Look in the upper-right corner of the first page. It begins with “CP” for automated notices or “LTR”/“Letter” for correspondence. That number identifies the notice type and is the key to knowing how to respond.
No. A CP2000 is a proposed adjustment based on information that does not match your return. You can agree and pay, or dispute it with supporting documentation by the deadline. It becomes an assessment only if you do not respond or the IRS finalizes it.
You may lose the chance to dispute the issue in the most favorable forum, and collection notices can advance toward a levy or lien. If you have missed a deadline, respond as soon as possible and ask about reinstating your rights or requesting a collection alternative.