What Is the Time Limit for Income Tax Assessment?

The IRS statute of limitations on tax assessment is generally three years from the date you filed your return, but several situations stretch that window to six years, keep it open indefinitely, or eliminate it altogether. The rule lives in 26 U.S.C. § 6501, and which version of the deadline applies to you depends on what’s on your return, what’s missing from it, and whether you filed at all.¹

The Three-Year Default

Under 26 U.S.C. § 6501(a), the IRS must assess any additional tax within three years after your return was filed.¹ Assessment is the formal recording of a tax liability on the IRS’s books. Once the three years run out, the IRS loses its authority to propose adjustments, issue deficiency notices, or take that tax year to court.

Filing early does not start the clock early. A return submitted in February for an April 15 due date is treated as filed on April 15.¹ For the 2025 tax year, the filing deadline falls on April 15, 2026.² If April 15 falls on a weekend or legal holiday, the due date shifts to the next business day, and the three-year period runs from that adjusted date.

If you file under an extension, the clock starts on the date you actually file, not on the original April 15 due date and not on the extended October date. File on August 10 under an extension, and the IRS has until August 10 three years later.

Amended Returns Don’t Restart the Clock

Filing an amended return does not reset the three-year period. The deadline stays anchored to the original return. One narrow exception applies: if the IRS receives a signed amended income tax return within the last 60 days before the assessment deadline expires, it gets an additional 60 days from receipt to assess any additional tax shown on that amendment.³ The mini-extension only covers the added tax on the amendment itself, and only for income tax returns.

Six Years for a Substantial Omission of Income

The window doubles when a taxpayer leaves off a large piece of income. Under 26 U.S.C. § 6501(e)(1)(A), the IRS gets six years if the omitted amount exceeds 25 percent of the gross income reported on the return.¹ The comparison is against gross income, not net profit or taxable income after deductions. Report $200,000 in gross income while actually earning $260,000, and the $60,000 omission clears the 25 percent threshold of $50,000. The longer deadline applies.

The same six-year rule kicks in for unreported income tied to foreign financial assets that should have been disclosed under FATCA, provided the omitted amount exceeds $5,000.¹ The much lower dollar threshold reflects the focus on offshore compliance.

No Time Limit at All

Two situations wipe out the statute of limitations entirely. They are narrow, but absolute.

Fraudulent Returns

When a taxpayer files a false or fraudulent return with intent to evade tax, the assessment period never expires.¹ Fraud here means more than a careless mistake or a misreading of a complex rule. Courts look for deliberate deception: two sets of books, fabricated deductions, hidden bank accounts, consistent understatements across multiple years. The IRS carries the burden of proving fraud, and the bar is high. A sloppy return full of honest errors does not trigger this exception, no matter how large the resulting underpayment.

No Return Filed

If you never file a return for a year, the clock never starts.¹ The IRS can assess taxes for that year decades later. This is where people get into serious trouble: they skip a year, assume enough time has passed, and then a notice arrives. Filing a return, even one you can’t fully pay, starts the clock and eventually delivers finality. Not filing never does.

Missing Foreign Information Returns

If you hold interests in foreign corporations, partnerships, trusts, or financial accounts, you may owe information returns alongside your income tax return. Leaving them out creates a separate assessment rule that catches many taxpayers off guard.

Under 26 U.S.C. § 6501(c)(8), the assessment period for your entire return stays open until three years after you actually provide the missing foreign information to the IRS.¹ The rule covers common international forms for controlled foreign corporations, foreign trusts, and specified foreign financial assets. The normal three-year clock never starts on any part of the return tied to that missing disclosure.

There’s one safety valve. If the failure to report was due to reasonable cause rather than willful neglect, the extended period applies only to the specific items related to the missing information, not the entire return.¹ Without reasonable cause, the whole return remains exposed indefinitely until the overdue form is filed.

Extending the Deadline by Agreement

During an audit, the IRS sometimes bumps up against the assessment deadline before the examination is done. When that happens, it will ask you to sign a consent form that pushes the deadline back. You are not legally required to agree, and the two forms it uses work very differently.

Form 872: Fixed-Date Extension

Form 872 extends the assessment period to a specific agreed date. You and the IRS both sign off on the new expiration, and the IRS has to finish its work by then. You can refuse, negotiate a shorter extension, or limit the extension to specific issues.⁴

Form 872-A: Open-Ended Extension

Form 872-A has no fixed expiration and keeps the assessment window open indefinitely until one side takes action to close it. Either you or the IRS can end it by filing Form 872-T, which triggers a 90-day countdown. After those 90 days, the assessment period closes.⁵ The open-ended nature is why tax professionals generally prefer Form 872 when the IRS will accept it.

If You Refuse to Sign

If you decline to extend, the IRS will typically issue a statutory notice of deficiency before time runs out, using whatever information it has at that point.⁶ That notice preserves the IRS’s right to assess and moves the dispute to Tax Court. The practical risk of refusing is that the IRS may propose adjustments on incomplete information rather than give you more time to make your case during the audit.

Assessment Is Not the Same as Collection

Assessment and collection run on two different clocks, and mixing them up is a common mistake. The assessment deadline governs how long the IRS has to decide you owe additional tax. Once tax is assessed, a separate 10-year clock under 26 U.S.C. § 6502 governs how long the IRS has to actually collect it by levy or lawsuit.⁷ That 10-year period, known as the Collection Statute Expiration Date, can be paused or extended by bankruptcy, an offer in compromise, an installment agreement request, a Collection Due Process hearing, or an innocent spouse request.⁸ The takeaway for anyone thinking about the assessment window: closing the assessment door does not close the collection door on tax that has already been assessed.

How Long to Keep Your Records

Your record-retention plan should match the longest assessment period that could realistically apply to you. Keep supporting documents for at least three years after filing as a floor. If you had significant self-employment income or complex investments where an understatement could clear the 25 percent threshold, six years is safer. If you hold foreign financial assets or have any unfiled foreign information returns outstanding, keep records until at least three years after those forms are properly filed.

Records tied to the cost basis of property you still own, such as a home or an investment account, deserve longer retention. Keep them for the life of the asset plus the applicable assessment period after you sell. The IRS can’t reach back to assess a sale from seven years ago if the three-year window has closed on that year’s return, but reporting the wrong basis on this year’s return puts this year’s assessment clock in play.

1
Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection
2
Internal Revenue Service. When to File
3
Internal Revenue Service. 25.6.1 Statute of Limitations Processes and Procedures
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Internal Revenue Service. Form 872 – Consent to Extend the Time to Assess Tax
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Internal Revenue Service. IRM 25.6.22 Extension of Assessment Statute of Limitations by Consent
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Internal Revenue Service. 4.8.9 Statutory Notices of Deficiency
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Office of the Law Revision Counsel. 26 USC 6502 – Collection After Assessment
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Internal Revenue Service. Time IRS Can Collect Tax