How do IRS letter codes work and what should I do when I get one?

IRS letters and notices use short codes (CP, LT, Letter, etc.) to summarize the purpose of the notice before you read the full text. Interpreting those codes correctly saves time and prevents unnecessary penalties or delays. Below I explain the most common codes, how to verify the letter’s authenticity, immediate steps to take, and how to escalate when needed.

Why the code matters

The code printed at the top or in the header of IRS mail is your first clue about the urgency and type of response required. Examples:

  • CP2000 = automated income mismatch (the IRS compared third‑party reported income to your return)
  • LT11 = collection (notice of intent to levy)
  • Letter 5071C = identity verification request when suspicious activity is detected

Knowing the code helps you prioritize action: some letters only require a quick response or documentation, others require immediate payment or formal appeals. For a full list of common letters and detailed guidance, see the IRS resource on Understanding IRS Letters and Notices (IRS.gov) [https://www.irs.gov/newsroom/understanding-irs-letters-and-notices].

How to verify the notice is real

Scammers often mimic IRS notices. Before you act, verify the correspondence:

  1. Compare the sender address and return envelope to past IRS mail — but don’t rely on addresses alone.
  2. Check the letter code and number against the official IRS website (search the code plus “IRS” on irs.gov).
  3. Use the contact information printed on the letter or visit irs.gov/contact for official phone numbers and office locations; do not use phone numbers or links in suspicious emails or texts.
  4. If the letter asks you to verify identity online, go directly to the IRS Identity Theft Central pages instead of following an email link: https://www.irs.gov/identity-theft-central.

For help distinguishing scams from legitimate notices, FinHelp’s guide on Recognizing Scam Notices vs. Genuine IRS Correspondence provides practical checking steps and examples: “Recognizing Scam Notices vs. Genuine IRS Correspondence” (FinHelp) [https://finhelp.io/glossary/recognizing-scam-notices-vs-genuine-irs-correspondence/].

Immediate steps to take (short checklist)

  1. Read the letter entirely and note the code and deadline.
  2. Verify legitimacy using irs.gov and the letter’s contact info.
  3. Gather supporting documents (W‑2s, 1099s, bank statements, previous tax returns).
  4. Respond in writing or via the method the letter specifies before the deadline.
  5. If money is owed but unaffordable, contact the IRS to discuss payment options right away.
  6. If you suspect identity theft, follow the IRS identity verification steps immediately.

For general practical steps you can follow for any IRS notice, consult FinHelp’s checklist: “What to Do When You Receive Any IRS Letter: A Practical Checklist” [https://finhelp.io/glossary/what-to-do-when-you-receive-any-irs-letter-a-practical-checklist/].

Common codes and how to respond (real-world guidance)

  • CP2000 (Underreported income or mismatch): Review the income items the IRS lists and compare them to your copies of W‑2s and 1099s. If the IRS is correct, sign the response form and pay or set up a payment plan. If you disagree, provide documentation (payer statements, corrected forms) and file a written rebuttal. For detailed steps, see FinHelp’s CP2000 resources: “How to Handle a CP2000 When You Disagree with the IRS” [https://finhelp.io/glossary/how-to-handle-a-cp2000-when-you-disagree-with-the-irs/].

  • LT11 (Final notice — intent to levy): This is a serious collection notice that typically follows prior reminders. If you receive an LT11, act immediately: call the IRS or your tax professional, request a collection alternative (installment agreement or Offer in Compromise if eligible), or request a Collection Due Process hearing if you qualify. FinHelp’s primer on LT11 explains options to stop levy actions: “LT11 Notice: Intent to Levy” [https://finhelp.io/glossary/lt11-notice-intent-to-levy/].

  • Letter 5071C (Identity verification): The IRS sends a 5071C when it flags possible identity theft on a return. Follow the instructions to verify your identity (online verification tool or phone). If you didn’t file the return, follow the IRS Identity Theft guidance and file an Identity Theft Affidavit (Form 14039) if directed. FinHelp’s step‑by‑step guide on responding to a 5071C is here: “How to Respond to an IRS Identity Verification Letter (Letter 5071C)” [https://finhelp.io/glossary/how-to-respond-to-an-irs-identity-verification-letter-letter-5071c/].

Real examples from practice

In my 15 years working with taxpayers, a common scenario is a CP2000 triggered by a payer’s data entry error. One client received a CP2000 reflecting an extra zero in a 1099 amount. We gathered a corrected 1099 and employer statement, sent a clear rebuttal with supporting documents, and the IRS adjusted the proposed change without penalty.

Another client received an LT11 after missing earlier notices. Acting quickly, we negotiated an installment agreement and filed the appropriate forms to stop the levy. In cases of 5071C identity checks, prompt verification usually clears the hold on a refund within weeks; delays occur when taxpayers ignore the letter or fail to produce acceptable ID documentation.

Documentation and recordkeeping tips

  • Keep a dedicated folder (physical or digital) for IRS correspondence by tax year.
  • Save copies of all returns, W‑2s, 1099s, and correspondence for at least seven years when you have itemized deductions, adjustments, or audit exposure.
  • If you respond to a letter, send documents by certified mail and retain the receipt.

In my practice I set up a simple document naming convention (YearTypeCode—for example, 2024CP2000response.pdf) so items are easy to retrieve during follow‑up.

Appeals, disputes, and timelines

Most notices include instructions for appeals or how to contest adjustments. Typical timelines vary by notice, but many collection actions allow a 30‑ to 60‑day window for appeal. Keep these rules in mind:

  • If you receive a statutory notice of deficiency (a separate, formal notice that may follow some letters), you generally have 90 days to file a petition in Tax Court.
  • For collection notices like LT11, you may have 30 days to request a hearing; check the notice for the exact deadline.

If you need to appeal, organize a clear timeline and compile documents showing why the IRS should change its position. FinHelp has articles on filing appeals and requesting collection hearings that explain the forms and procedural steps.

Common mistakes taxpayers make

  • Ignoring the notice and hoping it goes away — this often leads to levies, liens, and extra penalties.
  • Responding hastily without documenting the case — submit clear, organized evidence.
  • Using unofficial phone numbers or links from suspicious emails — always verify via irs.gov.

When to hire a tax professional

Consider professional help if:

  • The notice proposes a large tax increase or penalties you don’t understand.
  • A collection action is imminent (LT series letters).
  • You suspect identity theft or a fraudulent return has been filed in your name.

As a tax practitioner, I typically step in when the notice affects future tax refunds, includes substantial penalties, or when a levy is possible. A qualified CPA, enrolled agent, or tax attorney can negotiate with the IRS, request appeals, and prepare the necessary forms.

Additional authoritative resources

Quick reference table of common codes

Code General purpose Typical action required
CP2000 Automated income mismatch Review, document, and respond (dispute or pay)
LT11 Final notice — intent to levy Contact IRS/representative immediately; request alternatives
5071C Identity verification Verify identity promptly using IRS methods

Professional disclaimer: This article is educational and not personalized tax advice. For decisions about your specific tax situation, consult a qualified tax professional.

Related articles on FinHelp:

If you need help responding to a specific letter, bring the notice and related documents to your tax advisor or use the IRS contact information on the notice to get started.