A real IRS audit letter arrives by U.S. mail on Department of the Treasury stationery, carries a notice or letter number in the upper-right corner of the first page, names the tax year under review, lists the items the IRS is questioning, and prints a firm deadline for your response. If you’re trying to figure out what an IRS audit letter looks like because one showed up in your mailbox, the format itself is the first clue to whether the document is genuine and what kind of review you’re facing.
What a Genuine Letter Looks Like on the Page
The envelope is government-issued and shows a return address for a specific IRS processing campus or field office, not a generic P.O. box with no agency name. Inside, the letter is printed on plain white paper in standard government formatting, with the official seal of the Department of the Treasury or the Internal Revenue Service on the letterhead. The tone is bureaucratic. There are no colorful graphics, no marketing fonts, no handwriting on the envelope, and no urgent slogans.
The first page identifies you by name and taxpayer identification number, states the tax year at issue, and explains in plain language which parts of your return the IRS wants to examine. Somewhere on that first page, usually in the upper-right corner, is an alphanumeric code. That code is the single most useful piece of information on the letter, because it tells you exactly what type of contact this is.
The Notice or Letter Number Tells You Which Kind of Contact It Is
Not every letter from the IRS is an audit, and the code at the top separates them.
CP2000 is technically not an audit. It’s an automated notice sent when income or payment information reported to the IRS by an employer, bank, or other third party doesn’t match what you put on your return. The notice proposes adjustments, shows the information the IRS used to calculate them, and lets you agree, partially agree, or disagree.1Internal Revenue Service. Understanding Your CP2000 Series Notice
Letter 566 is the real thing: your notification that a return has been selected for examination. Variations exist. Letter 566S targets a specific item on your return, and Letter 566E focuses on wages, withholding, and refundable credits. The letter lists the items being questioned and asks for supporting documentation by a stated deadline.2Taxpayer Advocate Service. Initial Contact Letter
Letter 525, the “General 30-Day Letter,” arrives later in the process, after the IRS has reviewed your records and reached a conclusion. It presents the proposed changes, usually with Form 4549 attached, and gives you 30 days to agree or request an appeal with the IRS Office of Appeals.3Taxpayer Advocate Service. Letter 525
The code also signals whether the review will be handled entirely by mail (a correspondence audit) or whether the IRS may want an in-person meeting.4Internal Revenue Service. IRS Audits
What Comes Inside the Envelope
An audit letter rarely arrives alone. Several documents typically accompany it, and each has a distinct role.
Form 4549, titled “Report of Income Tax Examination Changes,” lists the tax year, identifies the line items the IRS wants to adjust, and shows a side-by-side comparison of the figures you reported against the figures the IRS proposes. It also calculates the additional tax, interest, and penalties that would follow if you accept the changes.5Internal Revenue Service. Audit Reconsideration Process for Correspondence Examination
Publication 1, “Your Rights as a Taxpayer,” is usually enclosed. It explains the Taxpayer Bill of Rights, including the right to be informed, the right to quality service, and the right to challenge the IRS’s position and be heard.6Internal Revenue Service. About Publication 1, Your Rights As A Taxpayer Read it. It sets out what the IRS is legally required to do while your case is open.
A response form is included as well, generally with checkboxes indicating whether you agree or disagree with the proposed changes. Correspondence audits sometimes add questionnaires about your business operations or specific expenses.
For correspondence audits, the specific document request often comes as Form 4564, “Information Document Request,” listing the records the examiner wants to see line by line.7Internal Revenue Service. Form 4564 – Information Document Request Each item on the request corresponds to a specific line on your return that the IRS has flagged. Common records include bank statements, receipts, cancelled checks, and business ledgers, and the request will usually name exact dates, dollar amounts, or transaction types.
How to Confirm It’s Not a Scam
The IRS makes first contact by mail. It does not open audits by phone, email, text message, or social media.8Internal Revenue Service. Ways to Tell if the IRS Is Reaching Out or if It’s a Scammer Any “audit notice” that reaches you through another channel isn’t one.
The fastest way to verify a physical letter is to log in to your IRS Online Account at irs.gov. Your account shows digital copies of notices sent to you, and for some correspondence audits you can view your audit status directly.9Internal Revenue Service. Online Account for Individuals If the letter doesn’t appear there, call the IRS at a number you look up independently (not one printed on a letter you suspect is fake) to confirm. You can also look up the notice or letter number on the IRS site under “Understanding Your IRS Notice or Letter” to see whether the type exists and what it covers.8Internal Revenue Service. Ways to Tell if the IRS Is Reaching Out or if It’s a Scammer
Warning signs of a fake: spelling errors or awkward grammar, links to sites that don’t end in “.irs.gov,” threats of arrest or immediate action, and demands to pay by gift card or wire transfer.10Internal Revenue Service. Know the Warning Signs of a Tax Scam A real audit letter never threatens arrest and never demands on-the-spot payment. It gives you a response window measured in weeks.
The Deadline and How to Respond
The response deadline printed on the letter is the most important detail on the page. For most correspondence audits, you get 30 days from the date of the letter. If you need more time, you can fax a written request to the number on the letter, and the IRS will ordinarily grant a one-time automatic 30-day extension.4Internal Revenue Service. IRS Audits
The letter itself tells you how to reply. Most notices offer three options: mail, fax, or digital upload. The IRS Document Upload Tool at irs.gov accepts JPG, PNG, and PDF files and sends confirmation of receipt. Some letters include a unique access code that routes your upload to the right examiner; if yours has one, use it within 70 days, because the code expires.11Internal Revenue Service. IRS Document Upload Tool If you mail your response, use a delivery method that provides tracking and delivery confirmation; the IRS specifically recommends requesting confirmation of receipt.4Internal Revenue Service. IRS Audits Certified mail with return receipt is the standard approach, and that receipt is your proof if there’s ever a dispute about timing.
Organize documents in the order they appear on the information request. Examiners work through many cases, and a well-organized response resolves faster. If a questionnaire came with the letter, complete every field before submitting.
What Missing the Deadline Costs
Ignoring the letter doesn’t make the audit disappear. The IRS will proceed with the information it already has, which almost always means the proposed changes stand and you owe additional tax. Interest then accrues on the unpaid balance; for 2026, the IRS charges 7% per year on underpayments, compounded daily.12Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026 If the balance remains unresolved, the failure-to-pay penalty adds 0.5% of the unpaid tax per month, up to 25%.13Internal Revenue Service. Failure to Pay Penalty
If the IRS determines the underpayment was due to negligence or careless disregard of the tax rules, an accuracy-related penalty of 20% of the underpayment applies on top of everything else.14Office of the Law Revision Counsel. 26 U.S. Code 6662 – Imposition of Accuracy-Related Penalty on Underpayments These stack.
Your Right to Have Someone Represent You
You don’t have to handle an audit alone. You can authorize an attorney, CPA, or enrolled agent to represent you. A representative can advocate on your behalf, negotiate with the examiner, sign documents, and receive copies of related IRS notices.15Internal Revenue Service. Power of Attorney and Other Authorizations You grant the authority by filing Form 2848, “Power of Attorney and Declaration of Representative.”
If the IRS schedules an in-person interview, you can stop it at any point to consult a representative, and the examiner is required by law to pause the interview and give you time to do so.16Internal Revenue Service. Taxpayer Representation You don’t need to have one lined up in advance.
Don’t Confuse the Initial Letter with a Notice of Deficiency
An initial audit letter (Letter 566, or a 30-day letter like Letter 525) is not the same document as a Notice of Deficiency. The Notice of Deficiency, sometimes called the “90-day letter,” comes later, only if the IRS’s proposed changes remain unresolved after the examination and appeals process. It starts a hard 90-day clock to file a petition with the U.S. Tax Court (150 days if you’re outside the country).17Internal Revenue Service. Understanding Your CP3219N Notice Missing that window generally means the Tax Court cannot hear your case,18Taxpayer Advocate Service. Filing a Petition with the United States Tax Court and your only remaining route is to pay in full and then sue for a refund. If the letter in your hand is an initial audit contact, you’re not on that clock yet. If it says “Notice of Deficiency” and gives you 90 days, mark the date the moment you open the envelope.