What Does an IRS Letter Look Like: CP Numbers and Red Flags

A real IRS letter looks plain and administrative: a white envelope with a Department of the Treasury return address, an “Official Business / Penalty for Private Use, $300” marking, a windowed address panel, and inside, a letter carrying the circular IRS seal, a notice or letter code (CP or LTR) in the corner, your name, and only the last four digits of your Social Security number. If you are asking what does an IRS letter look like because something arrived in your mailbox, the layout details below will tell you quickly whether it is genuine.

The Envelope

Genuine IRS envelopes are plain white. The return address shows the Department of the Treasury, then “Internal Revenue Service,” then the name of a specific processing center such as Austin, TX or Ogden, UT. Two phrases sit near that return address: “Official Business” and “Penalty for Private Use, $300.” That penalty language is a standard marking required on mail sent by federal agencies without prepaid postage.1Internal Revenue Service. 1.22.3 Addressing and Packaging

A transparent window on the front shows your name and mailing address. Sizes range from standard business envelopes to larger flat mailers depending on how many enclosures are inside. The design is deliberately plain. No colored logos, no marketing graphics, no urgent red stamps. An envelope covered in flashy design elements, or one whose return address does not reference the Department of the Treasury, should be treated with caution.

Certified Mail Means Open It Now

Most IRS letters arrive by regular first-class mail. Certain high-stakes notices must be sent by certified or registered mail, most notably the Notice of Deficiency, sometimes called the “90-day letter,” which proposes additional tax you owe. Federal law requires the IRS to send this notice by certified or registered mail to your last known address.2Office of the Law Revision Counsel. 26 U.S.C. 6212 – Notice of Deficiency A certified letter from the IRS almost always involves a deadline with serious consequences if missed. Open it immediately.

What the Letter Looks Like Inside

The top of the page carries official IRS branding. The IRS seal is circular, with “Treasury” across the top and “Internal Revenue Service” across the bottom, encircling a crest that includes justice scales and a key.3Internal Revenue Service. 1.17.7 Use of the Official IRS Seal, IRS Logo, and Program Logos Many letters also carry the IRS eagle logo alongside the text. Below the branding, “Department of the Treasury” and “Internal Revenue Service” appear in a standard typeface.

The header also shows the address of the specific IRS office that generated the letter and the date it was issued. That date matters, because response deadlines are counted from it. Depending on the notice type, you may have as few as 21 days or as many as 90 days, or 150 days if you live outside the United States, to take action.4Internal Revenue Service. Preparing a Request for Appeals The overall layout is rigid and administrative. No casual greeting, no decorative flourishes.

The CP or LTR Number in the Corner

Every IRS notice or letter carries a unique identification code, printed in the upper or lower right corner of the first page. Codes that begin with “CP” (such as CP14 or CP2000) identify automated notices generated by the IRS computer system.5Internal Revenue Service. Understanding Your CP2000 Series Notice Codes that begin with “LTR” identify letters drafted by an individual IRS employee, such as an examiner or collections officer. The code is set in a prominent font so it stands out from the body text, and on multi-page letters it repeats at the top of each page.

This number is the single most useful thing on the page. Searching it on irs.gov brings up a plain-language explanation of what the notice means and what to do about it.6Internal Revenue Service. Understanding Your IRS Notice or Letter If your number does not appear anywhere in that directory, the letter may be fraudulent.

How Your Personal Details Appear

The body of the letter ties it to your specific account. You will see your full name and a partially masked identification number. For security, the IRS displays only the last four digits of your Social Security number, employer identification number, or other taxpayer ID.7Internal Revenue Service. About Tax Transcripts Next to those identifiers, the letter names the specific tax year or tax period at issue.

If the letter involves a financial adjustment, the details usually sit in a structured table or bolded text block: the income, deduction, or credit the IRS believes was reported incorrectly, and the proposed change to your balance. Penalties appear as percentages rather than flat dollar amounts. The failure-to-file penalty, for example, starts at 5% of unpaid tax per month, up to a maximum of 25%.8Office of the Law Revision Counsel. 26 U.S.C. 6651 – Failure to File Tax Return or to Pay Tax Interest applies to unpaid balances and adjusts quarterly; for the second quarter of 2026, the underpayment rate is 6%.9Internal Revenue Service. Quarterly Interest Rates

What Else Is in the Envelope

Most IRS letters include more than the notice itself. Depending on the type, your envelope may contain:

  • Publication 1, Your Rights as a Taxpayer, a pamphlet summarizing the Taxpayer Bill of Rights, including your right to clear explanations, the right to appeal IRS decisions, and the right to pay only the correct amount of tax.10Internal Revenue Service. Taxpayer Bill of Rights 1: The Right to Be Informed
  • Notice 609, the Privacy Act Notice, explaining the IRS’s legal authority to collect your information, how it will be used, and what could happen if you do not provide it, such as the IRS disallowing credits, deductions, or exemptions on your return.11Internal Revenue Service. Notice 609 – Privacy Act Notice
  • A response form or worksheet, sometimes perforated for detachment, summarizing your account details and giving you space to indicate whether you agree or disagree. This stub may carry a scannable barcode or reference number so the IRS can route your reply correctly.
  • A detachable payment stub if you owe a balance, pre-printed with your account information and sized to fit a standard return envelope.

Near the bottom of the letter, a contact section lists a toll-free phone number, hours of availability, and a reference to irs.gov. Some letters name the specific employee or office that issued them, along with an employee ID number. If the notice involves an audit or appeal, this section states your response deadline and where to send your reply.

Red Flags of a Fake IRS Letter

Scammers sometimes send counterfeit IRS letters to trick people into sending money or sharing personal information. A few features give the fakes away.

  • Demands for gift cards, prepaid debit cards, cryptocurrency, or wire transfers. The IRS never asks for payment by these methods.12Internal Revenue Service. Gift Cards Are Never Used to Make Tax Payments
  • Threats of immediate arrest or of police or immigration officers being sent to your home. Real IRS letters do not threaten arrest.

    • li>Your full Social Security number printed on the page. Authentic IRS correspondence masks all but the last four digits.7Internal Revenue Service. About Tax Transcripts

  • No mention of your right to appeal or dispute. Every genuine IRS notice that proposes a change to your account explains how to respond.
  • A notice or letter code that returns nothing when you search it at irs.gov.

For an extra layer of confirmation, sign in to your IRS online account at irs.gov and see whether the notice appears on your record. If a matching balance or adjustment shows there, the letter is almost certainly real.13Internal Revenue Service. Online Account for Individuals

Once You’ve Confirmed It’s Real

Open the letter promptly and read it all the way through. Even if the contents are stressful, your response window starts from the date printed on the notice, not from when you got around to opening it.

  • Find the CP or LTR number in the corner and look it up on irs.gov to see exactly what the IRS is asking for.6Internal Revenue Service. Understanding Your IRS Notice or Letter
  • Check the deadline. Most notices give you 21 to 60 days to respond; a Notice of Deficiency gives 90 days (150 if you live outside the U.S.).4Internal Revenue Service. Preparing a Request for Appeals
  • Compare the notice against your records. If the IRS says income was underreported, check for a W-2 or 1099 you may have missed. If a deduction was disallowed, gather the documentation that supports it.
  • Respond in writing by the deadline even if you disagree. A written protest generally preserves your right to take the dispute to the IRS Independent Office of Appeals.4Internal Revenue Service. Preparing a Request for Appeals
  • Keep the original letter, your response, and any supporting documents together. If the issue escalates, you will need the paper trail.

Ignoring the letter does not make it go away. The IRS can automatically assess the proposed changes, add penalties and interest, file a federal tax lien on your property, or levy your wages and bank accounts. Letting a deadline pass can also permanently eliminate your right to challenge the IRS through an administrative appeal or in Tax Court.