How Far Back Can the IRS Audit Your Business?

The IRS can generally audit your business return for three years after you file it. That window opens to six years if you left more than 25% of your gross income off the return, and it stays open forever if the return was fraudulent or you never filed one at all. So the honest answer to how far back the IRS can audit your business is: usually three years, sometimes six, and in a handful of situations, without limit.

Which rule applies to you decides how long you need to keep records, how much risk still sits on a past return, and when you can finally close the book on a given tax year.

The Three-Year Default

The default rule is that the IRS must formally assess any additional tax within three years after your return is filed.¹ The word “assess” carries weight. It isn’t enough for the IRS to start looking within three years; the agency has to finish its examination and officially record the tax liability before the deadline passes. Internally, that date is called the Assessment Statute Expiration Date, or ASED.²

Once the ASED passes, the IRS can’t adjust your bill for that year, and you can’t claim a refund for it either.³ This three-year window covers the vast majority of business audits.

Six Years When You Omit More Than 25% of Gross Income

The IRS gets twice as long when a business leaves a large piece of income off the return. If the amount you omitted is more than 25% of the gross income you reported, the assessment window stretches to six years.¹ The comparison uses gross income, not net profit or taxable income, which matters for businesses with high revenue and thin margins.

The math is simple. Say your return shows $1,000,000 in gross receipts but you actually earned $1,300,000. The $300,000 you left off is more than 25% of the $1,000,000 you reported, which sits at a $250,000 threshold. The six-year window applies. Intent isn’t part of the test. An honest mistake that crosses the 25% line triggers the same extended clock as a deliberate one.

No Time Limit for Fraud or Unfiled Returns

Two situations remove the deadline entirely. If your return is false or fraudulent and you filed it with the intent to evade tax, the IRS can assess additional tax at any time.¹ This isn’t the same as an aggressive deduction or a defensible position that turns out wrong. The IRS has to show intentional wrongdoing: fabricated deductions, hidden income, double books. The burden of proving fraud falls on the government, and it’s a high bar. Once cleared, no clock runs.

The same unlimited timeline applies to any year where you never filed a return at all.¹ The statute of limitations only starts when the IRS receives a valid return. No return, no starting gun. A business that skipped its 2018 filing and hears from the IRS in 2030 has no statute-of-limitations defense. Small business owners get caught by this after tough years: a filing gets skipped, nothing happens for a while, and the exposure quietly stays open.

Payroll Taxes and Trust Fund Obligations

The no-limit rule bites hardest around payroll taxes. When a business withholds income tax and Social Security from employee paychecks and doesn’t send that money to the IRS, the unpaid amount is a trust fund tax. If the IRS finds a willful attempt to evade those trust fund obligations, there is no limitation period for assessment.⁴ The IRS can also pursue owners personally through the Trust Fund Recovery Penalty, making the individuals who controlled the employment tax decisions liable for the unpaid amount.

Extended Windows for Foreign Financial Assets

Businesses with overseas accounts or foreign holdings face their own extensions. If you’re required to report foreign financial assets on Form 8938 and you skip that reporting, the normal three-year clock on related tax items doesn’t begin running until three years after you actually provide the required information.⁵ If you never provide it, the window stays open indefinitely.

A separate rule pushes the assessment period to six years when you omit more than $5,000 in income tied to foreign financial assets that should have been reported under FATCA.⁵ The general Form 8938 reporting threshold in the statute is $50,000, though the IRS has set higher thresholds by regulation for certain filers.⁶ Any foreign bank account, foreign entity ownership, or foreign investment income should factor into how long you keep records.

When the Clock Actually Starts

The start date decides when your exposure ends, and it depends on when you filed.

File before the original due date, and the IRS treats the return as filed on the due date.¹ A C-corporation that submits on February 1 starts the three-year clock on April 15, not February 1. File after the deadline and the clock begins on the actual date the IRS receives the return.² Filing late pushes back the date your exposure ends.

Original due dates depend on the business type. Partnerships and S-corporations file by March 15 for calendar-year filers; C-corporations and sole proprietors file by April 15.⁷ When the date falls on a weekend or holiday, it shifts to the next business day.

Amended Returns Don’t Reset the Clock

Filing an amended return doesn’t restart the assessment period. It keeps running from the original filing date or the original due date. There’s one narrow exception. If the IRS receives an amended income tax return during the last 60 days before the assessment deadline expires, it gets an extra 60 days from receipt to assess additional tax shown on the amendment. The 60-day extension only applies to income tax returns, not employment, excise, or estate taxes.⁸

The IRS May Ask You to Extend the Deadline

When an audit is running and the three-year window is closing, the IRS will often ask you to sign Form 872 to extend the assessment deadline by mutual agreement.⁹ This happens more than most owners expect. Rather than rush out a deficiency notice, the agency asks for more time.

You can refuse.¹⁰ Declining has consequences, though. If the IRS can’t get an extension, it will typically issue a notice of deficiency based on whatever information it has, which may be less favorable than the result of a finished audit where you could explain deductions and provide documentation. The scope is negotiable, too. You can limit the extension to specific issues or a specific period rather than leaving it open-ended. It’s a judgment call, and agreeing often makes sense when you have a strong position you haven’t fully presented.

Collection Is a Separate 10-Year Clock

The assessment deadline is only half the picture. Once the IRS formally assesses additional tax, it has 10 years to collect. That collection deadline is the Collection Statute Expiration Date, or CSED.¹¹ Certain events pause or extend the 10-year period, including bankruptcy filings, offers in compromise, and installment agreement requests.

An audit that wraps up in year two of the three-year assessment window can still drive collection activity for another decade. A 2024 return assessed in 2026 could be actively pursued through 2036. The CSED is the real finish line.

How Long to Keep Business Records

Your record retention should match the longest window that could realistically apply to each year. The IRS recommends keeping records that support items on your return at least until the relevant statute of limitations expires.¹²

Three years is the minimum for any filed return where you reported all income accurately.
Four years for employment tax records, measured from the date the tax was due or paid, whichever is later.¹²
Six years if there’s any chance you underreported gross income by more than 25%.
Seven years if you claimed a deduction for worthless securities or bad debts.¹²
Indefinitely if you never filed a return for the year or the return was fraudulent.

For property your business owns, keep records until the statute of limitations runs on the year you sell or dispose of the asset. You’ll need them to calculate depreciation and figure gain or loss.¹² State audit windows can add to your retention burden. Most states run a three- or four-year assessment period for income taxes, but those periods often extend in the same situations the federal rules do: substantial omissions, fraud, and unfiled returns.

1
Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection
2
Internal Revenue Service. Time IRS Can Assess Tax
3
Internal Revenue Service. Statutes of Limitations for Assessing, Collecting and Refunding Tax
4
Internal Revenue Service. Trust Fund Recovery Penalty Assessments
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Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection
6
Office of the Law Revision Counsel. 26 USC 6038D – Information With Respect to Foreign Financial Assets
7
Internal Revenue Service. Starting or Ending a Business 3
8
Internal Revenue Service. 25.6.1 Statute of Limitations Processes and Procedures – Section: Amended Return
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Internal Revenue Service. Extension of Assessment Statute of Limitations by Consent
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Internal Revenue Service. Consent to Extend the Time to Assess Tax
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Internal Revenue Service. Time IRS Can Collect Tax
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Internal Revenue Service. How Long Should I Keep Records