The IRS can go back three years on most audits, six years if they find a substantial underreporting of income, and unlimited years if they suspect fraud.

The standard statute of limitations for the IRS to audit your return and assess additional tax is three years from the date you filed or the return's due date, whichever is later. This means if you filed your 2021 return on time in April 2022, the IRS generally has until April 2025 to start an audit. After that window closes, they cannot assess new tax on that year.

The three-year rule is the most common scenario. It applies when the IRS finds errors, disallowed deductions, or income you did not report — as long as the amount is not considered substantial. Most routine audits happen within this timeframe because the IRS has limited resources and prioritizes recent years.

Key Takeaways

  • The IRS has three years from your filing date to audit most returns and assess additional tax.
  • If the IRS finds you underreported income by 25 percent or more, they can go back six years instead of three.
  • There is no time limit if the IRS believes you committed tax fraud or did not file a return at all.
  • The clock starts from your filing date or the return's due date, whichever is later — not from when you owed the tax.
  • State tax agencies often have their own statute of limitations, which may be longer or shorter than the federal three-year window.

When the IRS can go back six years

If the IRS determines you underreported your gross income by 25 percent or more, the statute of limitations extends to six years. This is called the substantial underreporting rule. For example, if your actual income was $100,000 but you reported only $70,000, that is a 30 percent underreporting, and the six-year window applies.

The six-year rule does not mean the IRS will automatically audit you that far back. It means they have the legal right to do so if they discover the substantial underreporting during an audit of a more recent year. Once they find it, they can then examine the earlier years within that six-year window to see if the same pattern exists.

The IRS measures underreporting based on gross income reported on your return versus what they believe your actual gross income was. This includes wages, self-employment income, rental income, investment income, and other sources. Underreporting deductions or credits does not trigger the six-year rule — only income does.

Unlimited lookback for fraud or unfiled returns

If the IRS suspects you committed tax fraud, there is no statute of limitations. They can go back as far as they have records, which is often 10 years or more depending on what documents exist. Fraud means you intentionally and knowingly underpaid your taxes — not simply making a mistake or missing a deduction.

The IRS does not need to prove fraud in court to extend the statute of limitations. They only need to show in the audit process that there is a "substantial understatement of income attributable to fraud." This is a lower bar than criminal fraud, and it shifts the burden to you to prove you did not act fraudulently.

If you never filed a return for a particular year, the statute of limitations does not start. The IRS can assess tax on unfiled years indefinitely, though in practice they usually focus on the past 10 years. If you owe back taxes from unfiled years, the IRS can file a return on your behalf and assess the tax owed.

How the clock starts and stops

The statute of limitations clock starts on the later of two dates: the date you actually filed your return or the return's official due date. If you filed your 2023 return early in January 2024, the clock starts in January 2024. If you filed late in October 2024, the clock still starts in October 2024 — not in April when the return was due.

If you filed an extension, the clock starts from the extended due date, not the original April deadline. For example, if you filed a six-month extension for your 2023 return, the due date becomes October 15, 2024. If you then filed on October 10, 2024, the clock starts October 10, 2024 (or October 15 if you filed after the deadline).

The clock can stop or restart if you sign certain agreements with the IRS. If you agree to extend the statute of limitations — which the IRS often requests during an audit — you sign Form 872, and the deadline moves forward. You can refuse to sign, but doing so may prompt the IRS to issue a notice of deficiency and refer the case to appeals or court.

What happens after the statute expires

Once the statute of limitations expires, the IRS cannot assess additional tax on that return. If they send you a notice of deficiency after the deadline has passed, you can challenge it in Tax Court by arguing the statute has run. The IRS must prove they sent the notice before the deadline expired.

An expired statute does not erase the tax you owe if you actually underpaid. It only prevents the IRS from legally collecting it through assessment. In practice, this means the IRS cannot add penalties or interest after the deadline, and they cannot pursue collection actions like wage garnishment or bank levies for that year.

If you owe money and the statute expires, the IRS may still try to collect through other means — for instance, by offsetting a tax refund you are owed in a later year. The rules around collection are separate from the rules around assessment, and collection has its own timeline (usually 10 years from assessment).

State tax audits and their own timelines

State tax agencies are not bound by the federal statute of limitations. Each state sets its own rules. Some states follow the federal three-year standard, others allow four, five, or six years. A few states have no statute of limitations for fraud or unfiled returns, just like the IRS.

If you are audited by your state, ask the auditor which statute of limitations applies. The state may be able to go back further than the IRS, or they may have a shorter window. You will need to know this to understand which years are actually at risk and which are closed.

If both the IRS and your state audit you for the same year, they operate independently. The IRS audit does not stop the state audit, and vice versa. However, if the IRS makes a change to your federal return, you may be required to file an amended state return, which could reopen that year for state purposes.

Frequently Asked Questions

Can the IRS audit a return from 10 years ago?

Only if they suspect fraud or you did not file a return at all. For a normal audit with no fraud involved, the IRS is limited to three years (or six if they find substantial income underreporting). If 10 years have passed and there is no fraud claim, the statute has expired and they cannot assess additional tax.

Does filing an amended return restart the statute of limitations?

Filing an amended return does not restart the clock on the original return. The statute is based on when you filed the original return, not the amended one. However, if you amend a return within the statute period, the IRS can then audit both the original and amended versions within their window.

What if I filed my return late — does that change when the IRS can audit?

Yes. The statute starts from the date you actually filed, not the original due date. If you filed your 2022 return in September 2023 (late), the three-year window runs from September 2023, not from April 2023. Filing late actually gives you more time before the statute expires.

If the IRS is auditing me, can they look at years outside the statute of limitations?

Generally no, but they can look at earlier years if they find a pattern. If they are auditing your 2023 return and discover substantial income underreporting, they can then examine 2022, 2021, and 2020 (going back six years from 2023). They cannot, however, assess tax on years where the statute has already expired.

What should I keep my tax records for?

Keep your tax records for at least seven years. The IRS standard is three years, but the six-year rule for substantial underreporting and the 10-year collection statute mean older records can matter. Keeping seven years of receipts, bank statements, and supporting documents covers most scenarios without being excessive.