How Far Back Can the IRS Audit You?

Written by Sam Brotman, J.D., LL.M. (Taxation), MBA — Managing Attorney, Brotman Law  ·  Updated May 2026

The Short Answer

Most audits happen within two years of filing. A letter or notice arriving for a return you filed four years ago is unusual — but it can happen, and it usually means the IRS believes one of the extended rules applies. Understanding which rule is in play, and whether the IRS's position is actually correct, is where the analysis starts.

The rules below apply to federal income tax. California's Franchise Tax Board runs its own audit clock — four years as a standard, with different rules for federal adjustments and fraud. That's covered in the California section below.

The 3-Year Rule: IRC § 6501(a)

The three-year period applies to the vast majority of individual income tax returns. If you filed your 2022 return on time in April 2023, the IRS's standard window to audit that return closed in April 2026. A correspondence audit, office audit, or field audit that begins after that date cannot result in an additional assessment for 2022 under the general rule.

A few things worth understanding about how the three-year window works in practice:

• The clock runs from the later of the due date or the filing date. If you filed your 2022 return in February 2023 — earlier than the April 15, 2023 due date — the clock still doesn't start until April 15, 2023. The earlier filing date doesn't shorten the window for the IRS.
• Extensions don't reset the clock based on when you file. If you got an extension to October 15, 2023 and filed in August 2023, the three-year period runs from August 2023 — because that's the actual filing date, which is later than the original April 15 due date. The extension moved the due date, so it also moved when the clock can start if you file within the extension period.
• The IRS must assess tax within the period — not just start an audit. An audit that begins within three years but doesn't result in an assessment until after the statute has run is generally barred from collecting on the additional tax. The assessment date is what controls.

For a closer look at what happens during the examination itself, see our overview of IRS audits and how they work.

The 6-Year Rule: Substantial Omission of Income

The six-year rule is the one most taxpayers don't think about when they're deciding how long to keep records. Here's how the threshold works: the IRS compares the income you actually reported to the gross income that should have appeared on the return. If the omission exceeds 25% of what you reported, the extended statute applies — the IRS gets six years instead of three, and they can audit for the omitted amount and anything related to it.

A few situations that commonly trigger the six-year window:

• Unreported self-employment income. Independent contractors who don't receive 1099s, or who receive them but don't report all of them, are a common case. If the omitted amount pushes past 25% of reported gross income, the statute extends.
• Missing K-1 income. Partnership and S-corporation income that doesn't make it onto the return, either because a K-1 arrived late or the taxpayer didn't include it, can trigger § 6501(e) if the omission is large enough.
• Unreported foreign account income. Income from offshore accounts, foreign investments, or foreign entities that wasn't reported on the return is a well-worn path to the six-year period — and it has additional implications for FBAR and Form 5471 (covered below).
• Rental income omissions. Cash rental income that was partially or entirely not reported is auditable under the extended window if the omission crosses the 25% threshold.

One clarification that comes up often: the 25% calculation uses gross income as the denominator — not adjusted gross income, not taxable income, and not net income. Gross income for this purpose includes wages, interest, dividends, business receipts, rental income, and the rest. An omission that seems small relative to taxable income can still trigger the six-year rule if gross income is the right comparison figure.

See the types of IRS audits to understand how the IRS tends to approach extended-statute examinations differently from standard audits.

No Statute of Limitations: Fraud and Failure to File

This is not a theoretical provision. The IRS uses it. Tax fraud cases that come to light years after the fact — through informant tips, whistleblower disclosures, or related civil or criminal proceedings — can go back decades if the government can establish fraudulent intent.

Two separate scenarios fall under § 6501(c):

Fraudulent returns. The IRS must establish that the taxpayer filed a return with an intent to evade tax — not just that there were errors or omissions, but that there was willful fraud. This is a higher bar than mere negligence. But where fraud is established, the statute never runs. The IRS can reach back to any year, and the taxpayer has no SOL defense.

Failure to file. If you simply didn't file a return for a given year, the three-year clock never starts. There's no return to trigger the running of the statute. The IRS can assess tax for that year at any point in the future. This situation comes up regularly in delinquent filing cases and voluntary disclosure programs — taxpayers who haven't filed in years are not operating with any SOL protection for those years.

The difference between civil fraud (unlimited SOL, potential civil fraud penalty of 75% of the underpayment under § 6663) and criminal tax fraud (a separate matter governed by the criminal statute of limitations under 26 U.S.C. § 6531, generally six years) is worth understanding if you're dealing with potential exposure on both tracks. Civil and criminal proceedings run independently, and one does not automatically preclude the other.

How the Clock Is Actually Calculated

Here's how it plays out across a few common scenarios:

The practical takeaway: filing early doesn't give the IRS less time. The statute doesn't start running until the due date at the earliest. And filing late — whether within an extension or just delinquent — pushes the closing date out by exactly the same amount.

When in doubt about whether a year is open or closed, pull your IRS account transcript. The transcript shows the return received date and the date of assessment for any adjustments. Those dates are the inputs the statute calculation runs on.

What Tolls or Extends the Statute

Understanding what can toll the statute is important because the IRS will sometimes contact taxpayers near the end of a statute period asking them to extend. Here's what actually moves the clock:

Form 872 — Consent to Extend the Time to Assess Tax

Form 872 is a written agreement between the taxpayer and the IRS extending the time to assess tax. Taxpayers are not legally required to sign it. But in practice, if the IRS is auditing you and the statute is approaching, they will ask. If you refuse, the IRS typically issues a notice of deficiency (a "90-day letter") to lock in its position before the statute runs — which opens Tax Court as the next step, whether you want to go there or not.

Signing Form 872 gives the IRS more time to finish the audit and negotiate. Whether it's in your interest to sign depends on the specifics of the case. If the examination is progressing toward a reasonable resolution, extending can be sensible. If the IRS is on a fishing expedition with no real basis for the audit, refusing to sign and letting the statute run is a legitimate strategy — with the understanding that a statutory notice of deficiency will follow.

Bankruptcy

Filing for bankruptcy tolls the IRS assessment statute under IRC § 6503(h). The period is suspended during the pendency of the bankruptcy case plus 60 days after it concludes. This tolling can be significant in cases where a bankruptcy filing extends over years — the IRS's clock pauses during that period and picks up where it left off when the stay is lifted.

Pending Tax Court Litigation

Once the IRS issues a notice of deficiency and the taxpayer files a petition in Tax Court, assessment is stayed during the period the case is pending. The statute is also tolled for 60 days after the Tax Court's decision becomes final.

Foreign Asset Cases

If the IRS is examining a return that involves foreign financial accounts, foreign trusts, or foreign corporations, and the taxpayer has failed to file required information returns — such as Form 5471 (foreign corporation), Form 8938 (FATCA), or Form 3520 (foreign trusts) — the statute can be extended significantly. Under IRC § 6501(c)(8), the statute for the entire return does not begin to run until those required foreign information returns are filed. That is not a six-year rule — it is an open-ended suspension of the statute for the full return, not just the foreign income items.

Amended Returns: Does Filing One Restart the Clock?

This is a question that comes up a lot, and the short answer is that the act of filing an amendment itself doesn't give the IRS more time. If the original statute would have closed in April 2026, filing a 1040-X in January 2026 doesn't push that date to April 2029.

There is a meaningful exception worth knowing about. If the amended return discloses income that was not on the original return, and the total omission (original plus what's newly reported) crosses the 25% threshold under § 6501(e), the IRS can argue that the six-year extended statute applies to the amount now on the books — not just the newly disclosed amount. In practice, this is an argument the IRS makes; it is not settled in every circuit. But the risk is real.

There's also a separate consideration on the refund side. Under IRC § 6511, a taxpayer has either two years from the payment of tax or three years from the filing of the original return to claim a refund, whichever is later. An amended return filed outside that window can be filed — but the IRS won't process a refund from it. The refund statute and the assessment statute are different clocks running at the same time, and they don't move in sync.

The FBAR and Foreign Account Connection

FBAR violations under 31 U.S.C. § 5321 are not tax violations — they're Bank Secrecy Act violations administered by FinCEN (with enforcement delegated to the IRS). The civil FBAR statute of limitations is six years from the date the violation occurred. For willful failures to file, the penalty can reach the greater of $100,000 or 50% of the account balance per year of violation, with no ceiling on the total exposure.

The interaction between the FBAR statute and the income tax statute matters in practice because they're usually connected. A taxpayer with an undisclosed foreign account who failed to report income from that account is potentially facing:

• A six-year income tax SOL under § 6501(e) (large income omission), or an unlimited period if the conduct rises to fraud
• A separate six-year FBAR civil SOL running from each year's violation
• An additional exposure under § 6501(c)(8) if the required foreign information returns (Form 5471, 8938, 3520) were never filed — which suspends the income tax SOL for the full return

Foreign account cases are where the standard three-year assumption causes the most damage. Taxpayers who assume they're safe after three years because they've heard "the IRS has three years to audit you" are often wrong when the facts involve offshore accounts, foreign entities, or unreported foreign income.

California FTB Statute of Limitations

California's four-year standard SOL already runs longer than the federal three-year period, which means California audits can begin for years that are already closed at the federal level. That's not a theoretical problem — the FTB does audit years the IRS won't touch.

A few California-specific rules worth understanding:

Federal Adjustment Rule

When the IRS makes a final adjustment to your federal return — through an audit, an agreed deficiency, or a Tax Court decision — you are required to report that adjustment to the FTB within six months. From the date of that federal final determination, the FTB gets two years to assess additional California tax based on the federal change. This means the FTB can assess California tax on a federal adjustment even if the California four-year statute has already run. The federal final determination opens a fresh two-year window.

Fraud

For fraudulent California returns, there is no statute of limitations — same as federal. California Revenue and Taxation Code § 19057 has the same unlimited exception for fraud that IRC § 6501(c) has at the federal level.

No Return Filed

If no California return was filed, the California statute never starts running. The FTB can assess tax for any year in which a required return was not filed, at any time.

If you have both a federal and California tax situation that spans multiple years, the resolution strategy for each should account for both statutes running simultaneously. They don't always align, and a resolution that closes the federal matter may leave a California window wide open.

Audit Type and SOL Patterns

The IRS audits taxpayers through three main channels: correspondence audits, office audits, and field audits (also called revenue agent examinations). The statute of limitations is the same regardless of audit type, but the type of audit often signals where in the SOL period the IRS is acting — and why.

A correspondence audit that arrives two years after filing is routine. A revenue agent who contacts you 30 months into the three-year period, is auditing multiple years, and asks you to sign Form 872 — that pattern is different. That agent is working toward the end of the window on purpose, and whether to extend is a real decision that should be made with counsel.

For a breakdown of the different audit formats and what each involves, see our guide to types of IRS audits.

What Records to Keep and for How Long

The IRS doesn't set a formal record retention period — they just tell you to keep records as long as they may be needed for the administration of any provision of the Internal Revenue Code. That's not particularly useful guidance. Here's what actually makes sense:

• Seven years minimum for most individual returns. This covers the three-year SOL comfortably, and provides one year of buffer beyond the six-year extended period.
• Indefinitely for any year where you believe there may be fraud exposure. If there's any question about whether a year could be characterized as fraudulent — by the IRS or by you — there is no SOL running, and destruction of records can create its own problems.
• Indefinitely for assets you still hold. Cost basis records for real estate, stock, and other capital assets need to be kept as long as you own the asset plus seven years after you dispose of it. The IRS can audit the gain calculation years after the sale, and if the cost basis records are gone, the IRS's numbers control.
• Indefinitely for corporate, partnership, and trust returns where you have ownership interest. Basis calculations, passive activity losses, and capital account records run through years of prior returns. Destroying old records creates gaps that are difficult to reconstruct.
• Never destroy records if you have received or expect an IRS notice. Once you know an audit is possible for a year, destroying records for that year creates potential obstruction issues. The standard retention schedule doesn't apply once you have reason to believe a year is under review.

Received a Notice for a Year You Thought Was Closed?

The IRS's internal systems are not infallible. A notice can be sent in error for a year outside the statute. It can also be sent because the IRS believes the six-year rule applies, or because it's asserting fraud — in which case the notice is not necessarily wrong, just operating under a different set of rules than you expected.

When you receive a notice for a year you thought was closed, here's what to actually do:

1. Pull the original return and determine the exact filing date. The transcript will show it. Confirm whether you filed on time, late, or within an extension period.
2. Calculate the standard three-year period from the later of the due date or actual filing date. If that date has passed, the standard statute has run.
3. Review the return for any income omissions that could trigger the six-year rule. If the IRS is contacting you about unreported income, that's the first thing to check.
4. Check whether you signed any Form 872 consents for that year. If you did, the agreed extension date controls — not the original statute.
5. Do not respond to the IRS without understanding exactly which period is in play. Responding substantively without raising the statute as a defense waives it in some contexts.

If the statute has run and the IRS is still trying to assess additional tax, the right response is to raise the statute as a bar — not to engage on the merits of the underlying liability. Those are different arguments, and making one doesn't mean you have to make the other.

A tax attorney can pull your transcripts, confirm the relevant dates, and tell you whether the statute has run before you respond to anything. That's a 15-minute analysis, not a major undertaking.