IRS Audit Statute of Limitations: Three, Six, and Unlimited Years

The IRS generally has three years from the date you file a return to audit it and assess additional tax. That is the default IRS audit statute of limitations, and it applies to most returns filed accurately and on time. The window stretches to six years when a return omits a large amount of income, and it disappears entirely for fraud or for years you never filed at all.¹

The Three-Year Default

For most taxpayers, the IRS must assess any additional tax within three years after the return is filed. “Assess” means the agency formally records the amount you owe. If it doesn’t act within that window, it permanently loses the right to demand more money or impose penalties for that year.¹

The agency uses this period to cross-check reported income, deductions, and credits against W-2s, 1099s, and other third-party documents. If everything lines up, you never hear from them, and the year quietly closes.

When the Clock Actually Starts

The starting date depends on when your return is considered filed, and a few rules trip people up.

Filing early gets you nothing. A return filed before the due date is treated as filed on the due date. Submit your 2025 return in February 2026, and the three years still run from April 15, 2026 through April 15, 2029.²

Filing late or on extension pushes the finish line later, not earlier. If you use the automatic six-month extension and file on October 15, the three-year window starts that October date. In the IRS’s own example, a 2021 return filed on October 31, 2022 had an assessment expiration date of October 31, 2025.²

Keep a record of the exact date you filed. That date controls when your exposure ends.

The Six-Year Window for Large Income Omissions

When a return omits an amount that exceeds 25% of the gross income actually reported, the IRS gets six years instead of three. This applies whether the omission was deliberate or an honest mistake.¹

The math is straightforward. Report $100,000 in gross income when you actually earned $130,000, and the $30,000 omission is 30% of what you reported. The six-year rule applies. Had you omitted $24,000 (24%), the standard three years would still control.

For business owners, “gross income” here means total receipts before subtracting the cost of goods or services, not net profit. That broader denominator makes the 25% threshold easier to cross than many business owners expect.¹

Basis Overstatements on Property Sales

If you sell an asset and overstate your cost basis, thereby understating your gain, that overstatement counts as an omission from gross income for the six-year rule. The statute explicitly states that “an understatement of gross income by reason of an overstatement of unrecovered cost or other basis is an omission from gross income.” Inflate your basis enough to cross the 25% threshold and the IRS has six years to catch it.¹

Foreign Financial Assets

A separate six-year trigger applies to unreported income tied to foreign financial assets. Omit more than $5,000 in income connected to assets that should have been reported on Form 8938, and the extended window applies regardless of whether the omission exceeds 25% of your reported income.¹

If you fail to file the required foreign information reports at all, the statute of limitations cannot expire until three years after you finally furnish that information. The clock never starts running until you comply. This covers Form 8938 and several other international reporting forms.³

When There Is No Time Limit

In three situations, the statute of limitations disappears completely and the IRS can assess tax at any point, whether that’s five years or fifty years later:

Filing a false or fraudulent return with intent to evade tax.
Any willful attempt in any manner to defeat or evade tax.
Not filing a return at all. Without a filed return, the clock never starts, and the IRS can prepare a substitute return and assess tax, interest, and failure-to-file penalties at any time.

All three are set out in the statute itself.¹

Fraud brings more than an open-ended timeline. The civil fraud penalty adds 75% of the underpayment attributable to fraud on top of the tax owed, and criminal prosecution remains possible.⁴

The failure-to-file scenario catches more people than you might expect. Some taxpayers assume that years of silence from the IRS means they’re in the clear. They aren’t. Without a filed return, there is no triggering event to start any limitations period. Filing old returns, even years late, is what starts the clock and eventually creates a deadline.

If your spouse filed a fraudulent joint return without your knowledge, Innocent Spouse Relief may separate you from the unlimited assessment window. The relief is unavailable if you knowingly participated in the fraud or if the two of you transferred assets to each other as part of a fraudulent scheme.⁵

Events That Pause or Extend the Clock

Even within the three-year or six-year windows, several events can keep the assessment period open longer than the calendar suggests.

Signing Form 872

During an ongoing audit, the IRS may ask you to sign Form 872, which voluntarily extends the time to assess additional tax. The request usually comes when the audit is complex and the original deadline is approaching. You can refuse, limit the extension to specific issues, or negotiate an end date.⁶

Refusing isn’t always the strong move it sounds like. If the IRS runs out of time, it will typically issue a formal notice of deficiency based on whatever information it has, which may produce a larger proposed adjustment than you’d face if you cooperated. The question is whether you’d rather give the auditor more time to get the number right or force a potentially inflated assessment you’d then need to challenge in Tax Court.⁷

The 90-Day Letter

When the IRS determines you owe additional tax, it mails a statutory notice of deficiency, commonly called a 90-day letter. This notice pauses the statute of limitations. Once mailed, the IRS cannot assess the tax during the 90 days you have to petition the Tax Court (150 days if you’re outside the United States), plus an additional 60 days after that period ends. If you do petition the Tax Court, the statute stays frozen until the court’s decision becomes final.⁸

The 90-day deadline to petition is absolute. The IRS cannot extend it, and missing it means the proposed deficiency gets assessed as stated.

Third-Party Summons Challenges

If the IRS issues a summons to a bank, employer, or other third party for records related to your tax liability, and someone challenges that summons in court, the assessment clock pauses while the legal challenge runs. The suspension lasts from the date the challenge is filed until all appeals are resolved. If the third party simply doesn’t respond and the summons isn’t resolved within six months, the statute is also suspended until there’s a final resolution.

Assessment Is Not Collection

The clock for assessing tax and the clock for collecting it are two different things, and confusing them is a common mistake. Assessment is when the IRS determines you owe money. Collection is when it actually comes to get the money through levies, wage garnishments, or lawsuits.

Once a tax liability is assessed, the IRS has 10 years to collect. After that, the debt becomes legally unenforceable and collection activity must stop.⁹

That 10-year window can be extended if you enter an installment agreement with a written extension of the collection period, or if the IRS files a court proceeding to collect. It can also pause when you file for bankruptcy or submit an offer in compromise. Even so, taxpayers with old assessed liabilities sometimes find the debt expires on its own if the IRS hasn’t collected within the window.

Matching Your Records to the Limitations Period

Your record retention strategy should mirror whichever tier applies to you. The IRS’s guidance:¹⁰

Three years covers most taxpayers. Keep records supporting income, deductions, and credits for at least three years from the filing date.
Four years for employment tax records, running from when the tax becomes due or is paid, whichever is later.
Six years if there’s any concern you may have underreported income by more than 25% of the gross income shown on the return.
Seven years for records supporting a worthless securities loss or bad debt deduction.
Indefinitely if you didn’t file a return or filed a fraudulent one. There’s no limitations period to expire, so no safe point to discard the documents.

Property records deserve extra care. Keep documentation of your cost basis, improvements, and depreciation for any property you own until at least three years after you file the return for the year you sell or dispose of it. For property received in a tax-free exchange, keep records for both the old and new property until the limitations period expires for the year you dispose of the replacement.¹⁰

When in doubt, keep it. Storing a few extra years of documents costs far less than facing an audit without them.

1
Office of the Law Revision Counsel. 26 U.S.C. 6501 – Limitations on Assessment and Collection
2
Internal Revenue Service. Time IRS Can Assess Tax
3
Office of the Law Revision Counsel. 26 U.S.C. 6501 – Limitations on Assessment and Collection
4
Office of the Law Revision Counsel. 26 U.S.C. 6663 – Imposition of Fraud Penalty
5
Internal Revenue Service. Publication 971, Innocent Spouse Relief
6
Internal Revenue Service. Form 872-B, Consent to Extend the Time to Assess Tax
7
Internal Revenue Service. Internal Revenue Manual 25.6.22 – Extension of Assessment Statute of Limitations by Consent
8
Office of the Law Revision Counsel. 26 U.S.C. 6503 – Suspension of Running of Period of Limitation
9
Office of the Law Revision Counsel. 26 U.S.C. 6502 – Collection After Assessment
10
Internal Revenue Service. How Long Should I Keep Records