IRS Letter 566

What Letter 566 is and who sends it

Letter 566 is the first letter of an audit by mail, which the IRS calls a correspondence examination. The Taxpayer Advocate Service (TAS) files it under “Letter Notifying Taxpayer of Audit with Request for Additional Information” and says it is “your notification that your tax return has been selected for an audit.” It lists the items being questioned and asks you to document them.

It comes from the IRS campus units that run mail audits. Their manual (IRM 4.19.13, effective January 23, 2026) tells examiners who only need information to use the program’s own first letter “or utilize Letter 566-S, Initial Contact.” It is not a bill or a collection notice.

TAS lists a dozen versions, from 566 (IN/PR) to 566-T. The ones you are most likely to see:

Earned Income Tax Credit audits usually start with a CP75 instead (IRM 4.19.20). Other numbers are in our guide to IRS audit letters.

Why you got Letter 566

TAS says the IRS accepts most returns as filed but “selects some for an additional review or audit,” and that selection “doesn’t automatically mean something is wrong.” Publication 3498 names statistical scoring, links to another taxpayer’s audit and mismatched third-party forms as the main reasons; see types of IRS audits.

A mail audit is usually narrow. IRS program procedures use Letter 566-S to ask for support of items such as Schedule C car and truck expenses, repairs, the Clean Vehicle Credit (Form 8936), employee business expenses and the Child Tax Credit (IRM 4.19.15). The items listed on your letter are the scope you need to answer.

A CP2000 is different: it comes from income matching, and TAS says it “is not an IRS audit or a bill.”

What comes with the letter

A Letter 566 package usually contains:

• The items under examination, by tax year, usually with a list of documents that prove each one.
• Questionnaires, in some audits; TAS says to complete them and send them with your documents.
• Reply instructions: address, fax number, contact phone, the response date and, on some letters, an upload access code or secure messaging link.
• Form 4549, Report of Income Tax Examination Changes, only in the 566-B and 566-J versions. TAS says the report shows “the potential outcome of the audit if you don’t provide information supporting the items in question.”

If the letter’s contact number is 866-897-0177 or 866-897-0161, the IRS says your IRS Online Account shows the audit under “Records and Status,” including the next due date.

Your deadline and how to get more time

The date printed on your letter is the deadline. TAS says to provide the documents “by the due date on the letter.” For the combined 566-B and 566-J letters, TAS says you have “30 or 45 days (from the date of the letter)”; your letter shows which.

Asking for more time. For audits by mail, the IRS audits page says to fax a written request to the number on the letter, or mail it if you can’t fax, and that “we can ordinarily grant you a one-time automatic 30-day extension.” The IRS manual adds detail:

• The first request is granted automatically and adds 30 days to the original response date on Letter 566-S or 566-T (IRM 4.19.13.11.7).
• Campus examiners confirm the new date in writing with Letter 686-B.
• No extension is granted if 180 days or less remain before the assessment statute expires, unless you agree to extend the statute and the facts warrant it.

Your options

If records are the problem, our guide to an IRS audit with missing records covers what the IRS accepts and how to reconstruct amounts. Never create or backdate a document.

How to respond to Letter 566

1. Confirm the letter is real. The IRS says it “won’t initiate an audit by telephone.” Check your IRS Online Account or call 800-829-1040 (IRS.gov, 2026), not a number on a letter you doubt. See how to spot a fake IRS letter.
2. Mark the due date with a reminder a week earlier.
3. Pull your return and transcripts. Compare each listed item with your return as filed and your wage and income transcript (see reading IRS transcripts).
4. Gather copies, item by item, and label each document with the item it supports. Leave out papers the letter doesn’t ask for.
5. Write a short cover letter with your name, taxpayer ID, tax year, letter number and date, and a numbered list of enclosures. Use our audit response cover letter template.
6. Send it the way the letter allows: mail with delivery confirmation, fax with your name and Social Security number on every page, the IRS Document Upload Tool (JPG, PNG or PDF, with a receipt confirmation) or secure messaging on 566-T and 566-J.
7. Keep a full copy and proof of delivery. Publication 3498-A says the IRS will send a letter within 30 days acknowledging documents received by mail or fax.

What happens after you respond

TAS says that once the examiner reviews your documents, the IRS will “1) request more information, 2) accept your original tax return as filed, or 3) propose changes to your return.”

• Accepted as filed. Publication 3498-A says you get a letter saying the return is accepted. Keep it with your tax records.
• More information needed. The examiner writes or calls with what is still missing.
• Changes proposed. You receive Letter 525, the general 30-day letter, with Form 4549 and an explanation of each change. That is your chance to agree, send more proof or request Appeals.

No reply at all leads to the same Letter 525 once the waiting period ends (IRM 4.19.13.13). Ignore that too and Letter 3219, the notice of deficiency, follows: 90 days (150 if addressed outside the United States) to petition the Tax Court.

Mistakes to avoid

• Sending originals. Publication 3498-A says, “Please do not send original documents.”
• Signing a 566-B or 566-J report you disagree with. Publication 3498-A says not to sign the agreement page “if you disagree or plan to appeal.” Signing gives up your appeal rights for those changes.
• Missing the Appeals window on combo letters. TAS says to request an Appeals conference before the response date.
• Sending a box of everything. Answer the list; unrelated papers slow the review.

Doing it yourself, free help, and representation

A Letter 566 with a few items and records in hand can usually be answered without a professional. Help is worth considering for business income, missing records, large amounts or several years.

• Low Income Taxpayer Clinics can represent eligible taxpayers in audits and appeals for free or a small fee (find a clinic).
• Taxpayer Advocate Service helps for free when an IRS problem is causing financial difficulty or normal channels have failed: 877-777-4778 (IRS.gov, 2026).
• A representative (attorney, CPA or enrolled agent) can answer the letter for you under a Form 2848. See audit representation.

Global Gate Tax Relief offers a free consultation and, if it takes the case, quotes a flat fee upfront. No outcome is guaranteed. Request a free review of your Letter 566 or call 1-877-800-8180.

Frequently asked questions

Keep reading in the IRS Audit Guide

• IRS audit letters explainedEvery audit letter and form, with deadlines.
• First steps after an audit letterA 10-day checklist for any audit letter.
• Types of IRS auditsMail, office and field audits compared.
• Audit with missing recordsHow to rebuild and support amounts.
• Letter 525The 30-day letter that follows a mail audit.
• Audit response cover letterA template for sending your documents.