How Far Back Can the IRS Audit You?
Key Takeaway
The short version is that “how far back” has four different answers depending on your facts, and the difference between them is the difference between a closed year and a decade of exposure.
The three-year rule and where it starts
IRC § 6501(a) gives the IRS three years from the later of the return’s due date or its actual filing date. File your 2025 return on April 15, 2026, and the assessment window generally closes April 15, 2029. File in October under extension, and the clock starts in October. In practice most audits open 12–24 months after filing — the IRS rarely uses the full window for routine exams
When does the window stretch to six years?
Under IRC § 6501(e), omitting more than 25% of gross income doubles the window to six years. Since 2015, an overstatement of basis that produces the same understatement counts too — Congress wrote that into the statute after the Supreme Court said otherwise in Home Concrete. Foreign-asset omissions above $5,000 tied to Form 8938 reporting carry their own six-year rule. This is the trap for people with substantial unreported 1099 income, missed K-1s, or aggressive basis positions.
What has no time limit at all?
Two things: fraud, and silence. A false or fraudulent return with intent to evade leaves the year open forever — IRC § 6501(c)(1). And a year with no return filed never starts the clock — § 6501(c)(3). This is why the standard advice for non-filers is counterintuitive but correct: filing starts the statute; not filing preserves the exposure indefinitely. Our penalties chapter covers what attaches when old years get opened.
Audit clock vs. collection clock
Assessment and collection are different statutes with different lengths. The audit (assessment) window is § 6501’s three/six/unlimited ladder. Once tax is assessed, § 6502 gives the IRS ten years to collect — the CSED. A return audited in year three can produce a balance collectible into year thirteen. The CSED chapter covers that second clock and what pauses it.
How to check your own clock
Your IRS account transcript shows the assessment date (transaction code 150) each year — the anchor for both statutes. Pulling transcripts is free and takes minutes. If a year you thought was closed has drawn a letter, or an old unfiled year is surfacing, that’s a defense posture question — see audit defense, and note the California difference: the FTB runs four years, not three.
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Frequently Asked Questions
Can the IRS audit me after 3 years?
Yes, in three situations: a six-year window applies if you omitted more than 25% of gross income (or overstated basis to the same effect), there is no time limit for fraud, and there is no time limit for years where no return was filed.
Does filing an extension change the audit clock?
The three-year clock runs from the later of the due date or the date you actually filed. Filing in October under extension starts the clock in October — an extension doesn’t shorten or lengthen the window itself.
How far back can California audit compared to the IRS?
The FTB generally has four years instead of three — and like the IRS, no limit for unfiled returns. State and federal clocks run independently, and an IRS adjustment reopens the California year via required reporting.
Is the audit deadline the same as the collection deadline?
No — this is the most common confusion. Assessment (audit) generally ends at three years under IRC § 6501; collection runs ten years from assessment under IRC § 6502. A timely audit can start a collection clock that runs another decade.
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