IRS audit guide: how audits start, run and end

What is an IRS audit?

An IRS audit, which the IRS formally calls an examination, is a review of your accounts and records to confirm that a return follows the tax law and reports the right amount of tax. It is a check of specific items, not an accusation. The IRS says that being selected does not by itself mean an error was found (IRS, IRS audits).

The IRS audit process has three possible endings: no change (your return is accepted as filed), agreed (you accept the proposed changes and sign), or disagreed (you dispute the changes and can take them to a manager, mediation, the Independent Office of Appeals or the Tax Court). Everything on the pages in this section fits somewhere along that path.

How will the IRS tell me I am being audited?

The IRS tells you about an audit by letter sent to the address on your latest return or the address the IRS has on file. The IRS states that it will notify you by mail and will not initiate an audit by telephone. An unexpected call, text or email that claims you are under audit and demands payment is a scam signal, not an audit notice.

The letter names the tax year, lists the items under review and gives a reply date. Mail audits usually start with a Letter 566 variant, while in-person audits usually start with an appointment letter such as Letter 2205. Our page on the IRS audit letter shows how to read one and how to confirm it is genuine, and the Letter 566 page covers the most common mail version.

Mail, office and field audits: which kind do you have?

The IRS runs audits in three ways: by mail (a correspondence audit), in an IRS office (an office audit) or at your home, business or representative's office (a field audit). The type is set by the IRS and is shown in the first letter. Mail audits are by far the most common for individuals.

According to the IRS Data Book for fiscal year 2025, the IRS closed 441,578 examinations of individual income tax returns, and 393,767 of them, about 89%, were correspondence audits (IRS Data Book, Table 3-2). The remaining 47,811 were field examinations, a category the IRS uses for audits done in person by revenue agents and tax compliance officers.

Why are returns selected for an IRS audit?

The IRS selects returns in three ways: random selection, computer screening that compares a return against statistical norms for similar returns, and links to another taxpayer's audit, such as a business partner or investor. The IRS builds those norms from its National Research Program studies.

Separately, the IRS matches your return against Forms W-2, 1099 and other third-party reports. A mismatch usually produces a CP2000 proposal rather than a full examination. Our page on IRS audit triggers looks at selection in detail, including published audit rates by income level.

How far back can an IRS audit go?

The IRS generally includes returns filed within the last three years in an audit, and it says it usually does not go back more than six years even when it finds a substantial error. The legal limit for assessing extra tax is normally three years from the date the return was filed, under Internal Revenue Code section 6501.

That window stretches to six years when more than 25% of gross income was left off the return, and it never closes for a fraudulent return or a year with no return at all. The IRS audit statute of limitations page breaks down each exception and how long to keep records.

What happens during an IRS audit, step by step?

1. Letter arrives. Note the reply date and the items listed. Mark the date on your calendar the day it arrives.
2. Gather records. Pull receipts, bank statements, Forms 1099 and W-2, logs and anything else that supports the items named. Send copies, never originals.
3. Respond or meet. For a mail audit, send documents by the deadline. For an office or field audit, attend the appointment or send a representative.
4. Review the findings. The IRS either accepts the return, or sends a report of proposed changes, often Form 4549, Report of Income Tax Examination Changes.
5. Agree or disagree. Sign the report if you agree. If you disagree, ask for a manager conference or an appeal before the date on the 30-day letter.
6. Closing. An agreed case closes and any balance is billed. An unagreed case ends with a notice of deficiency that opens the door to the Tax Court.

If you already have a notice of deficiency, the 90-day clock is running. Read our page on the notice of deficiency before doing anything else.

How long does an IRS audit take?

There is no fixed length. The IRS says the time depends on the type of audit, how complex the issues are, how quickly information is provided, scheduling, and whether you agree with the findings. Its mail audit guide, Publication 3498-A, says audits closed with complete documents or a signed agreement can finish quickly, while others can take several months.

For mail audits the IRS can usually grant a one-time automatic 30-day extension if you need more time to gather records. Our page on how long an IRS audit takes explains what speeds a case up and what stretches it out.

Can I appeal an IRS audit result?

Yes. If you disagree with the examiner's proposed changes, you can ask to speak with the examiner's manager, request mediation, or file an appeal with the IRS Independent Office of Appeals, which is separate from the office that audited you. For a proposed change of $25,000 or less per tax period, a short small case request or Form 12203, Request for Appeals Review, is enough.

Above $25,000, you need a formal written protest. The IRS appeals process page walks through both. If you missed the audit or have new documents after it closed, audit reconsideration may reopen the case. If you receive a notice of deficiency, you can file a Tax Court petition within 90 days for a $60 filing fee, and a waiver is available.

Do you need IRS audit representation?

You have the right to represent yourself or to authorize someone else to represent you. Attorneys, certified public accountants and enrolled agents have unlimited rights to represent taxpayers before the IRS, including at Appeals. You authorize them with Form 2848, Power of Attorney and Declaration of Representative.

Representation is most useful when the amount at stake is large, the audit covers a business, or fraud or unfiled years are involved. Publication 3498-A notes that if you ask to consult a representative during an interview, the IRS must in most cases stop and reschedule. People with income at or below 250% of the federal poverty guidelines may qualify for free or low-cost help from a Low Income Taxpayer Clinic, generally for disputes under $50,000.

Pages in the audits and appeals section

• IRS audit triggers: how returns are picked and what the published audit rates show.
• How long an IRS audit takes: timing for each audit type and extensions.
• IRS audit statute of limitations: the 3-year, 6-year and no-limit rules.
• Correspondence audit: the mail audit from first letter to closing.
• Office audit and field audit: in-person examinations.
• IRS audit letter, Letter 566 and Letter 525: reading the letters.
• Audit reconsideration: reopening a closed audit.
• IRS appeals process and Tax Court petition: disputing the result.