What are IRS Notice Codes and why do they matter?

When you open a letter from the IRS, the small code in the upper right corner is not decorative — it’s a purpose-built signal. IRS notice codes (often starting with letters like CP, CPB, LT, LTR, or numbered series) identify the notice type, explain the general reason it was sent, and narrow what you must do next.

This quick reference teaches you how to read the code, what common codes mean, how to verify a notice, and the practical next steps I use when helping clients. I’ve worked as a tax advisor for over 15 years and have found that recognizing the code shortens response time, reduces stress, and often prevents penalties or escalations.

How to read the code and the notice

  • Location: The code usually appears at the top right of the first page. It may be separated into a short label (e.g., CP2000) and an internal notice number.
  • Prefixes: “CP” = Computer Paragraph (common correspondence); “LT” or “LTR” = letter series; numeric-only codes are also used for specific actions.
  • Read the subject lines and the first paragraph: the notice body will explain the reason and give a deadline or date by which you should act.
  • Look for contact instructions: many notices specify how to respond (mail, call, or submit documentation). Follow those instructions exactly.

Cite authoritative guidance: see IRS, “Understanding Your IRS Notice or Letter” (https://www.irs.gov/individuals/understanding-your-irs-notice-or-letter).

Common IRS notice codes and what they typically mean

Below are frequently seen codes with practical notes based on common cases I handle.

Notice Code Typical Meaning Immediate action I recommend
CP2000 Proposed changes to a return because reported income doesn’t match IRS records (W-2s/1099s). Don’t ignore. Compare the IRS information to your records. If correct, pay or set up an agreement; if wrong, respond with documentation. See our guide on responding to CP2000. (Responding to a CP2000).
CP501 / CP503 Balance due notices (escalating reminders). Verify account balance at IRS.gov or in your IRS Online Account, pay or request an installment plan to stop further notices.
CP10303 / Audit notice Notification that the IRS intends to examine a return. Gather records, review the audit scope, consider professional representation.
105 / Notice 105 Request for additional information on a specific return line. Provide the requested documents by the deadline.
LT11 / Letter 11 Notice of intent to levy (serious collection step). Act immediately: request a call, consider collection alternatives or representation.

Note: This table is illustrative, not exhaustive. For a broader list, see the IRS notice index: https://www.irs.gov/. The IRS provides individual pages for many common notices (for example the CP2000 page at https://www.irs.gov/individuals/notice-cp2000).

Step-by-step: What to do when you receive any IRS notice

  1. Pause and read—don’t panic. The first paragraph will state the reason and any deadlines.
  2. Verify authenticity (do not click links in suspect emails). Confirm legitimacy using guidance at FinHelp: “How to Verify the Authenticity of an IRS Notice” (https://finhelp.io/glossary/how-to-verify-the-authenticity-of-an-irs-notice) and on IRS.gov.
  3. Check the code and match it to the notice explanation.
  4. Review your records. Pull tax forms, W-2s/1099s, bank statements, receipts, and prior-year returns.
  5. Respond in writing when requested. Send copies, not originals. Keep proof of mailing or secure digital copies.
  6. If money is due and you agree, pay or set up an installment agreement. If you disagree, prepare a written response and attach supporting documentation.
  7. Use IRS tools: view account information or request transcripts through IRS Online Account or Get Transcript at IRS.gov to confirm details and dates.

I often tell clients: simple documentation and a timely, documented response resolves most notices.

Real-world examples and timelines

  • Example 1 (CP2000): A client received a CP2000 claiming $4,300 of unreported income from a 1099. After we pulled bank deposits and a corrected 1099 from the payer, we returned a signed response with evidence. The IRS adjusted the proposed change and removed penalties. (IRS CP2000 procedures are summarized at https://www.irs.gov/individuals/notice-cp2000.)

  • Example 2 (CP501): A taxpayer ignored the first balance-due notice and later received a CP503 and a late fee. When we intervened, the taxpayer qualified for an installment agreement; having a plan stopped most additional collection activity.

Timelines: many notices require action within 30–60 days, but some collection notices may give fewer days. Always check the exact deadline on the notice.

How to verify a notice and get official records

  • Mail is the primary IRS delivery method for notices. The IRS will not initiate a first contact demanding immediate payment via email or phone (scams do). See IRS guidance on scams and how the IRS contacts taxpayers.
  • To verify content, sign into your IRS Online Account or request a transcript at Get Transcript (https://www.irs.gov/individuals/get-transcript). These official tools show account history and can confirm whether the notice matches IRS records.
  • For walkthroughs and red flags to spot a scam, read our checklist: “How to Verify the Authenticity of an IRS Notice” (https://finhelp.io/glossary/how-to-verify-the-authenticity-of-an-irs-notice).

When to involve a tax professional or attorney

  • Complex adjustments (large CP2000 proposed changes or notices involving back taxes for multiple years).
  • Audit or collection notices (audit letter, Notice of Intent to Levy, Notice of Federal Tax Lien).
  • When deadlines are short and your documentation is incomplete.

In my practice, involving a CPA or tax attorney early prevents mistakes. A professional can prepare an organized response, communicate with the IRS on your behalf (with a Form 2848 Power of Attorney), and help negotiate installment agreements or offers in compromise where appropriate.

For hands-on case tracking and timelines, see our companion article: “How to Track Your IRS Case: Tools, Timelines, and What Each Notice Means” (https://finhelp.io/glossary/how-to-track-your-irs-case-tools-timelines-and-what-each-notice-means/).

Common mistakes taxpayers make

  • Ignoring the notice. Silence can escalate collection activity.
  • Calling the number on a suspicious email or clicking embed links—scammers mimic IRS language. Verify through IRS.gov or official transcripts.
  • Sending incomplete documentation or originals.
  • Assuming all fees are final. You can often appeal or provide evidence to change the IRS position.

Quick-response checklist (printable)

  • Note the notice code and deadline.
  • Verify authenticity via IRS Online Account or Get Transcript.
  • Match IRS-reported income to your forms.
  • Gather supporting docs (W-2s, 1099s, receipts).
  • Respond in writing; keep copies.
  • Pay, request payment relief, or dispute with evidence.
  • Get professional help if unsure.

Frequently asked practical questions

How are notices delivered? The IRS primarily mails notices to the address they have on file. If the mailing address is wrong, a notice can be delayed or lost. See IRS guidance on address updates.

Can you request a duplicate? Yes — you can view or request transcripts to see the information that prompted a notice.

Is every notice an audit or levy threat? No. Many notices are informational or propose a minor change. The notice type and code indicate severity.

Sources and further reading

Professional disclaimer: This article is educational and does not replace personalized tax advice. Tax law and IRS procedures change; consult a qualified tax professional or the IRS for guidance tailored to your situation.

In my practice, timely, documented responses prevent most notice escalations. Use this reference to decode the message, gather evidence, and choose the right next step.