If an IRS letter arrives questioning a return you filed years ago, the natural reaction is, "Can they even go back that far?" The answer depends on what is on the return. The IRS works under a statute of limitations for audits — but several exceptions can stretch or eliminate it.
What is the standard IRS audit lookback period?
For most taxpayers, the IRS generally has three years from the date you filed a return to audit it and assess additional tax. This is the Assessment Statute Expiration Date (ASED). If you filed early, the clock typically starts on the return's due date. The IRS confirms this in Topic No. 305, Recordkeeping and its guidance on how long to keep records.
When can the IRS go back 6 years?
The three-year window doubles to six years when you substantially understate your income — specifically, when you omit more than 25% of the gross income reported on your return. The same six-year period can apply to certain large omissions of foreign income or assets. This is why underreporting is so consequential: it does not just risk penalties, it keeps the audit window open far longer.
When is there no time limit at all?
In two situations, the IRS has unlimited time to audit and assess:
- You never filed a return. The clock never starts, so the IRS can act at any time. If you have unfiled returns, there is no statute protecting you.
- The return was fraudulent. Filing a false or fraudulent return with intent to evade tax removes the time limit entirely.
No return, no clock
The single most important takeaway: the statute of limitations only starts when you file. Skipping a return to "stay off the radar" actually leaves you exposed forever. Filing — even late — starts the clock that eventually protects you.
IRS audit time limits at a glance
| Situation | Lookback period |
|---|---|
| Standard return | 3 years |
| Income understated by more than 25% | 6 years |
| Certain unreported foreign income/assets | 6 years |
| Fraudulent return | No limit |
| No return filed | No limit |
How is the audit statute different from the collection statute?
These are easy to confuse. The audit (assessment) statute limits how long the IRS has to add tax to a return. The separate collection statute (CSED) gives the IRS 10 years to collect tax once it has been assessed. So a return audited near the end of the three-year window can still result in a debt the IRS may collect for a decade. We cover the collection side in our guide to statute of limitations exceptions.
How long should I keep my tax records?
Because of these windows, a practical recordkeeping rule protects you:
- Keep most records for at least 3 years after filing.
- Keep them 6 years if there is any chance you under-reported income by 25% or more.
- Keep records indefinitely if you did not file or filed a fraudulent return.
- Keep records tied to property for as long as you own it plus the period above, to support basis and depreciation.
What should I do if I am being audited for an old year?
First, verify the years in question and confirm the IRS is within its statute — sometimes it is not. Then respond on time with organized documentation. If the audit covers years you cannot fully support, professional audit representation can limit the damage and keep the examiner focused only on the legally open years. Knowing what drew attention also helps — see our guides to IRS audit triggers and audit red flags.
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Start Your Free ConsultationThe bottom line
For most people the IRS audit window is three years, extending to six for big income omissions and never closing for unfiled or fraudulent returns. Filing accurately and on time both starts the clock and keeps the window short — the best audit defense there is.
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About the author
This article was written by the certified tax team at US Certified Tax Services — IRS enrolled agents and tax professionals who resolve federal and state tax debt every day. It is general information, not legal or tax advice. For guidance on your specific situation, request a free consultation.