The IRS can go back three years for most audits, six years if it suspects you underreported income by 25 percent or more, and indefinitely if it believes you filed a fraudulent return or did not file at all.

The time limit for an audit is called the statute of limitations. It is the deadline after which the IRS cannot assess additional tax on a return you have already filed. The length of that deadline depends on what the IRS finds — or suspects — during the audit.

The three-year window is the most common. It runs from the date you filed your return or the return's due date, whichever is later. If you filed your 2021 return on April 15, 2022, the three-year clock started then. The IRS cannot audit that return after April 15, 2025, unless one of the longer time limits applies.

Key Takeaways

  • The IRS has three years from the filing date to audit most returns, which is the standard statute of limitations.
  • The time limit extends to six years if the IRS believes you underreported your income by 25 percent or more.
  • There is no time limit if the IRS suspects fraud or if you did not file a return at all.
  • The clock starts from your filing date or the return's due date, whichever comes later, not from the tax year itself.
  • If you file an amended return, a new statute of limitations may begin on that amended return.

When the IRS can go back six years

If the IRS finds that you left off more than 25 percent of your gross income on your return, it can extend the audit window to six years. This is called the substantial underreporting rule. The six-year period still starts from your filing date, not from the tax year.

The 25 percent threshold is measured against what you actually reported, not against what you should have reported. If you reported $40,000 in income and the IRS finds you omitted $15,000, that is a 37.5 percent underreporting — well above the 25 percent bar. The IRS would then have six years to assess tax on that $15,000 plus interest and penalties.

This rule applies only to income underreporting. Claiming deductions you should not have claimed, or overstating deductions you did claim, does not trigger the six-year window. The IRS still has three years to audit those issues.

When there is no time limit at all

The statute of limitations disappears entirely if the IRS believes you committed tax fraud. Fraud means you deliberately and knowingly filed a false return — not a mistake, not a misunderstanding of the rules, but intentional deception. The IRS does not have to prove fraud to the criminal standard; it only has to show it more likely than not that you acted with fraudulent intent.

If the IRS opens a fraud investigation, it can go back as many years as it wants. There is no cutoff date. The IRS can audit returns from 10, 15, or 20 years ago if it has evidence of a pattern of fraud.

Similarly, if you did not file a return at all for a given tax year, the statute of limitations never starts. The IRS can demand that return and assess tax on it at any point. This applies even if you filed returns for other years — each unfiled year is a separate matter with no deadline.

How amended returns restart the clock

If you file an amended return using Form 1040-X, you may restart the statute of limitations on that return. The new three-year (or six-year, or unlimited) period runs from the date you file the amendment, not from the original filing date.

This matters because it can extend the IRS's audit window. If you originally filed your 2020 return in April 2021, the three-year window would normally close in April 2024. But if you file an amended 2020 return in March 2024, the statute of limitations restarts and does not close until March 2027. The IRS then has a fresh three years to audit the amended return.

The IRS can also use an amended return against you. If you file an amendment that increases your tax liability, the IRS may use that as a starting point for a broader audit of that year.

What happens if the statute of limitations expires during an audit

The IRS must complete its audit and send you a formal notice before the statute of limitations runs out. Simply starting an audit does not stop the clock. If the IRS has not finished its work and issued a Notice of Deficiency (also called a 90-day letter) before the deadline, it generally cannot assess additional tax after that date.

However, the IRS can ask you to sign a consent form to extend the statute of limitations. This is called a Form 872 or a Form 872-A. Signing it gives the IRS more time to finish the audit. You are not required to sign, but if you refuse, the IRS will often close the audit and issue whatever information it has reached so far.

If you are in an active audit and the deadline is approaching, you should know your rights. You can ask your tax professional or the IRS directly how much time remains.

The difference between the audit statute and the collection statute

The statute of limitations for auditing a return is separate from the statute of limitations for collecting the tax the IRS says you owe. The IRS has 10 years from the date it assesses the tax to collect it through wage garnishment, bank levies, or liens.

This means the IRS could audit a 2015 return in 2024 (within the three-year window), find you owe $5,000, and then have until 2034 to collect that $5,000. The audit deadline and the collection deadline are two separate clocks.

Frequently Asked Questions

Can the IRS audit a return from 10 years ago?

Only if it suspects fraud, if you did not file a return for that year, or if you filed an amended return more recently. For a standard audit with no fraud involved, the IRS has three years from your filing date. A return filed in 2014 would be outside that window by 2024.

Does the statute of limitations reset if I file an extension?

No. The statute of limitations runs from your filing date or the return's due date, whichever is later — not from when you actually file. If your 2023 return was due April 15, 2024, the three-year clock starts April 15, 2024, even if you filed an extension and did not submit the return until October 2024.

What should I do if the IRS asks me to sign Form 872?

Form 872 extends the statute of limitations, giving the IRS more time to audit. You can sign it, refuse it, or negotiate a shorter extension. If you refuse, the IRS will close the audit based on what it has found so far. Consult a tax professional before signing, especially if the audit is complex or the IRS has already proposed significant changes.

If I owe back taxes, how long does the IRS have to collect?

The IRS has 10 years from the date it assesses the tax to collect it. This is separate from the audit deadline. Even if the audit statute expires, the collection statute continues running. The IRS can use liens, levies, and wage garnishment during this 10-year window.

Does the statute of limitations apply to state taxes too?

No. State tax agencies have their own statutes of limitations, which vary by state. Some states follow the federal three-year rule; others allow four, five, or six years. Contact your state tax agency or a tax professional to learn the deadline for your state.