The IRS can audit returns from the past three years in most cases, but can go back six years if it finds a substantial underreporting of income, and has no time limit if it suspects fraud.

The length of time the IRS can examine your tax returns depends on what they find — or suspect. Most audits happen within three years of when you filed, which is called the standard assessment period. But that window stretches if the IRS believes you underreported your income by 25 percent or more, or if there are signs of fraud or a missing return. Understanding which lookback period applies to you matters because it determines how far back you need to keep records and how much exposure you actually have.

Key Takeaways

  • The IRS has three years from the filing date to audit most returns, which is the period you should keep records for.
  • The lookback period extends to six years if the IRS finds you underreported gross income by 25 percent or more on a single return.
  • There is no time limit for audits involving fraud, criminal activity, or a completely unfiled return.
  • The clock starts from your filing date, not the tax year itself, so a 2022 return filed in April 2023 has a different deadline than one filed in October 2023.
  • Amended returns and installment agreements can restart or extend the audit window in specific situations.

The Three-Year Standard Period for Most Audits

For the vast majority of audits, the IRS has three years from the date you filed your return to begin an examination. This is the statute of limitations on assessment. If you filed your 2022 return on April 15, 2023, the IRS generally cannot start an audit after April 15, 2026. After that date passes, the IRS loses the right to assess additional tax on that return.

This three-year window is why the IRS recommends keeping records for at least three years. You need receipts, bank statements, invoices, and other documentation to support what you reported if an audit does happen. The IRS will ask you to prove the income, deductions, and credits you claimed, and you cannot do that without the original documents.

The three-year period applies whether you filed on time or late. What matters is the actual filing date, not the tax year. If you filed your 2022 return in October 2023 because you got an extension, your three-year window runs from October 2023, not from April 2023.

The Six-Year Extension for Substantial Income Underreporting

If the IRS discovers that you reported less than 75 percent of your actual gross income on a return, the statute of limitations extends to six years. This is called the substantial underreporting exception. The threshold is 25 percent of the income you should have reported — not 25 percent of the tax owed, but the actual income amount.

For example, if your true gross income was $100,000 but you reported only $70,000, that is a 30 percent underreporting, and the six-year period applies. The IRS can now audit that return up to six years from the filing date instead of three. This extension applies only to that specific return and only if the underreporting meets the 25 percent threshold.

The IRS does not need to prove you did this intentionally. Negligence, carelessness, or honest mistakes can trigger the six-year rule if the math shows a substantial underreporting. However, the IRS must identify the underreporting during the three-year window to use the six-year extension — they cannot discover it in year five and then claim they have until year six to examine it.

No Time Limit for Fraud or Unfiled Returns

If the IRS suspects fraud, there is no statute of limitations. The IRS can audit a return from 1995 if it has evidence that you deliberately misrepresented your income or claimed false deductions to evade taxes. Fraud is a serious allegation and requires evidence of intent to deceive, not just a mistake or negligence.

Similarly, if you never filed a return for a particular year, the IRS has no deadline to assess tax for that year. The statute of limitations does not start running until a return is filed. If you owe taxes for 2015 and never filed, the IRS can still pursue you for that year. This is one reason why filing a return — even a late one — can sometimes be strategically important.

Criminal fraud investigations operate under different rules than civil audits. If the IRS refers your case to the Criminal Investigation division, the lookback period depends on the specific charges, but the general principle is the same: fraud has no time limit.

How Amended Returns and Installment Agreements Affect the Timeline

If you file an amended return, you restart the statute of limitations on that return. Filing an amended 2022 return in 2025 starts a new three-year clock from the amendment filing date. This can work in your favor if you are correcting an error, but it also means the IRS gets a fresh window to examine that year.

If you enter into an installment agreement with the IRS to pay back taxes, the agreement itself does not extend the audit period. However, if you are still making payments when the statute of limitations would normally expire, the IRS may ask you to agree to extend the period. This is called a Statutory Notice of Deficiency extension, and you can refuse it — but refusing may complicate your payment arrangement.

What Triggers an Audit and How the Timeline Matters

The IRS selects returns for audit through computer screening, random selection, or because of specific red flags like unusually high deductions, business losses, or income that does not match third-party reports like W-2s or 1099s. Once selected, the IRS must begin the examination within the applicable statute of limitations. If they miss the deadline, they lose the right to assess additional tax.

Knowing the timeline matters because it affects your negotiating position. If you are in year five of a standard audit and the IRS has not formally begun the examination, you may have grounds to argue the statute has run. However, the IRS can extend the period if you agree to it, and many taxpayers do agree without realizing they do not have to.

Keeping Records Beyond Three Years

While three years is the standard recommendation, there are reasons to keep records longer. If you are self-employed or own a business, the IRS may look more closely at your returns, and the six-year rule is more likely to apply. If you claimed a loss that carried forward to future years, records from the loss year may be relevant to audits of later years.

For real estate, investments, or other assets with long holding periods, keep records for at least three years after you sell the asset. The IRS can audit the year you sold it, and you will need the original purchase documentation to prove your cost basis and calculate the gain or loss correctly.

Frequently Asked Questions

Can the IRS audit a return after I have already been audited for that year?

Yes, the IRS can audit the same year again if new information comes to light or if the first audit did not examine all issues. However, they cannot re-examine items that were already settled in the first audit unless there is fraud or a substantial error. The statute of limitations still applies to the second audit.

Does filing an extension change when the three-year period starts?

No. The three-year period runs from the date you actually file the return, not from the original due date. If you file an extension and submit your return on October 15 instead of April 15, the three-year clock starts from October 15. Filing on time versus late does not change the length of the period, only when it begins.

What happens if the IRS sends me a notice after the statute of limitations has expired?

If the IRS sends a notice after the statute has run, you can challenge it by arguing the assessment is time-barred. You would typically do this in response to the notice or by filing a claim for refund if you have already paid. Having the filing date documented is critical to proving the statute has expired.

If I owe back taxes, does the audit period extend while I am paying?

The audit period itself does not automatically extend, but the IRS can ask you to agree to extend it as a condition of setting up a payment plan. You can decline the extension, though this may complicate negotiations. If you do not agree to extend, the IRS must collect within the original statute period.

Does the six-year rule apply if I underreported deductions instead of income?

No. The six-year extension applies only to substantial underreporting of gross income, not to overstated deductions or credits. If you claimed deductions you should not have, the three-year standard period applies unless the IRS can prove fraud.