How Long Can the IRS Audit You? 3, 6, or Forever

Taxpayers often hear “three years” and stop thinking. In practice, the IRS has different clocks for different mistakes. Understanding when the assessment period ends helps you decide how long to keep basis records, when an old year is truly “closed,” and when you should still fix a return.

TL;DR

General rule: The IRS usually has 3 years from the date you file a valid return to assess additional tax.
Substantial omission of income: 6 years can apply if you omit more than 25% of gross income stated on the return (specific rules apply; see IRS guidance).
No return or fraud: Different rules can extend or suspend the clock; fraud has no fixed expiration like the three-year rule.
State taxes have their own statutes; do not assume they match federal.

This article focuses on federal concepts at a high level. Always confirm current law and your facts with a professional for your situation.

When the clock starts

For a typical Form 1040, the measurement usually starts when you file. If you file before the due date, the IRS may treat the start as the due date of the return for these purposes (a nuance that matters in edge cases).

Late-filed returns and amended returns can interact with the statute in ways that are fact-specific. If you are considering a 1040-X, ask how it affects your specific years.

The three-year window (simple model)

Imagine you filed your 2024 return on time in 2025. In many cases, the IRS’s window to assess additional tax for 2024 would be roughly three years from the filing date (subject to the “due date” rule above). That is why many advisors keep supporting records at least through that window.

The six-year window (substantial understatement)

If gross income is understated on the return and the omitted amount exceeds 25% of gross income reported, a six-year period may apply. This is why investment income that never made it onto the return can be especially costly: the IRS may have more time to assess once the issue surfaces.

Do not try to self-diagnose the 25% test from a blog post. Use it as a prompt to reconcile all 1099s every year.

Fraud, false returns, and no return

If a return was never filed, or if fraud is established, the usual three- or six-year models may not protect you from assessment for those years. This is one reason voluntary compliance (filing, paying, fixing mistakes) matters.

What you should keep (practical)

Even after three years, you may still need:

Purchase and improvement records for real estate until you sell.
Stock and option basis until positions are fully closed and the return year is settled.
Loan documents for basis in partnerships and certain investments.

Document proof callout: For brokerage sales, your 1099-B may not tell the whole basis story. Keep supplemental equity statements and trade confirmations until you are confident the statute has expired on the gain calculation.

Worked example: “Am I safe after three years?”

You omitted a 1099-MISC side gig in Year 1. You realize it in Year 4.

Do not assume the IRS cannot assess; facts matter, and state rules differ.
The clean move is often to file a correct original or amended return and pay what is owed, with interest.

FAQ

Does an audit extend the statute?
Certain actions (signing extensions, pending litigation, bankruptcy) can toll (pause) the clock. Read any Form 872 extension you sign.

Does state follow federal?
Often no. California and other states have their own periods and rules.

How to act on this today

Whether you are pre-filing or post-filing, verify your numbers against W-2s and 1099s so you never rely on “probably fine after three years.” Register to build a documented file for the current year.

Educational content only—not individualized tax advice.