Every audit runs against a statutory clock. Section 6501 of the Internal Revenue Code limits how long the IRS has to assess additional tax on a return — and once it expires, the year is closed. Three clocks exist: 3 years for a normal return, 6 years for a substantial omission of income, and no limit at all for fraud or a return that was never filed.
General information, not tax or legal advice. Which clock applies to an old year is a legal determination with real money on it; if the IRS is reaching back more than three years, have the period checked before you hand over records.
Do not confuse this clock with the IRS’s 10-year collection period, which starts at assessment and governs how long an existing tax bill can be collected — a different statute, owned by the Currently Not Collectible cluster. This page covers only how far back an audit can reach.
| Your situation | IRS deadline to assess |
|---|---|
| Ordinary filed return | 3 years from the later of the filing date or the due date |
| You omitted more than 25% of the gross income stated on the return | 6 years |
| You omitted more than $5,000 of income attributable to specified foreign financial assets | 6 years |
| False or fraudulent return filed with intent to evade tax | No limit |
| No return filed | No limit — the clock never starts |
| You signed a written extension (Form 872) | Whatever extended date you agreed to |
The general period runs from the date the return was filed — but with a deeming rule: a return filed before its due date is treated as filed on the due date. File your 2025 return on March 1, 2026 and the clock still runs from April 15, 2026, expiring April 15, 2029. File late, and the clock runs from the actual filing date instead. A return filed on extension starts the clock on the date the IRS actually receives it, and employment-tax returns are deemed filed on April 15 of the following year (§6501(b)(2)). Internally the IRS tracks the deadline as the Assessment Statute Expiration Date (ASED), which you can find on your IRS account transcript for the year (see what triggers an audit for how returns get picked inside that window).
The period doubles when you omit from gross income an amount properly includible that exceeds 25% of the gross income stated on the return. Concrete numbers: say you reported $80,000 of gross income — omitting $25,000 more is a 31% omission (the IRS gets six years); omitting $15,000 (19%) leaves the 3-year clock in place. Three refinements matter:
For a false or fraudulent return filed with the intent to evade tax, §6501(c)(1) lets the IRS assess at any time. And where no return was filed (§6501(c)(3)), there is nothing for a clock to run from — every unfiled year is permanently open. “No limit” does not mean “no proof,” though: the IRS must still prove fraud, and an honest mistake is not fraud. This is the honest answer to “am I safe after six years?”: six years closes a filed, substantially-honest return. It does nothing for an unfiled one.
When an audit is still open near the deadline, the examiner may ask you to sign Form 872, consenting to extend the assessment period. Practical points:
How far back can the IRS audit you? The clock limits assessment, and the audit has to finish inside it: generally the IRS must assess additional tax within 3 years after your return is filed (§6501(a)). Six years if you omitted more than 25% of the gross income stated on the return, and no limit at all for a fraudulent or unfiled return.
Can the IRS audit you after 10 years? For a filed, non-fraudulent return, no — the 3-year (or 6-year) assessment period closed long before, and the 10-year figure people quote is the separate collection period after assessment. But there is no time limit where no return was filed, or a return was false or fraudulent with intent to evade tax (§6501(c)) — those years never close.
What is the Assessment Statute Expiration Date (ASED)? The IRS’s name for the last day it can assess additional tax for a given year — the end of your §6501 clock. For a 2024 return filed on April 15, 2025, the ASED is April 15, 2028. Your account transcript shows a year’s ASED — the date examiners work backwards from when they ask for a Form 872 extension.
Does filing an amended return restart the audit clock? No. An amended return does not restart the original clock — the original filing date controls the 3-year (or 6-year) period. (The deadline for claiming a refund is a different clock again, under §6511.)
Sources: IRC §6501(a), (b), (c), (e); IRS, “IRS audits” (irs.gov); IRS Publication 1035, “Extending the Tax Assessment Period.” Currency verified 2026-10-23.