The IRS can audit returns from the past three years in most cases, but can go back six years if it finds a substantial underreporting of income, and has no time limit if it suspects fraud.
The three-year window is the standard statute of limitations — the legal deadline after which the IRS generally cannot assess additional tax on a return you filed. This clock starts from the date you filed your return or the return's due date, whichever is later. If you filed early, the three years runs from the due date. If you filed late, it runs from the date you actually filed.
The IRS does not randomly choose which years to audit. It typically focuses on recent returns because records are fresher and the money owed is more recent. But the agency can and does look further back when specific circumstances apply — and understanding those circumstances matters because they change what you should keep and how you should respond if contacted.
Key Takeaways
- The IRS has three years from your filing date to audit most returns, but this deadline extends to six years if income was underreported by 25 percent or more.
- There is no time limit for audits involving fraud, criminal activity, or a completely unfiled return.
- The statute of limitations can be extended if you sign an agreement with the IRS or if the agency issues a formal notice of deficiency.
- Keeping records for at least six years protects you if the IRS questions deductions or income from earlier years.
When the IRS can look back six years instead of three
If the IRS finds that you underreported your gross income by 25 percent or more, the statute of limitations extends from three years to six years. This is called the substantial underreporting rule. The IRS calculates this by comparing what you reported to what it believes you actually earned, based on documents like W-2s, 1099s, bank deposits, or third-party records.
The six-year window applies to the entire return, not just the underreported income. So if the IRS opens an audit for substantial underreporting, it can examine all your deductions, credits, and reported income for that year, even items that were reported correctly.
This rule catches situations like unreported cash income, side gigs not listed on your return, or rental income that was never disclosed. It also applies if you failed to report income from investments or business activity. The IRS does not have to prove intent — underreporting by 25 percent or more triggers the longer window automatically.
Fraud and unfiled returns have no time limit
If the IRS suspects tax fraud — meaning you deliberately and knowingly underpaid taxes — there is no statute of limitations. The agency can audit returns from decades ago. Fraud is a serious allegation and requires evidence of intentional wrongdoing, not just mistakes or negligence.
Similarly, if you never filed a return for a particular year, the IRS can assess tax for that year at any time. There is no deadline because the statute of limitations only applies once a return is filed. The IRS can use information from employers, banks, or other sources to reconstruct what you owed and bill you for it, plus penalties and interest.
Criminal prosecution for tax evasion also has no time limit in most cases, though the IRS typically pursues criminal cases only for the most serious violations involving large amounts of money or deliberate schemes.
How the statute of limitations can be extended or paused
The three-year or six-year window does not always run straight. The IRS can extend the deadline if you sign a consent form, usually called a Form 872 or Form 872-A. These forms give the IRS extra time to complete an audit. You are not required to sign, but the IRS may pursue the audit more aggressively if you refuse, and refusing can signal that you have something to hide.
The statute of limitations also pauses if you file an appeal or if the IRS issues a formal Notice of Deficiency (also called a 90-day letter). Once the IRS sends this notice, you have 90 days to file a petition in Tax Court. During that period and any subsequent appeal, the clock stops running.
If you and the IRS reach a settlement agreement, the statute may be extended as part of that deal. Always ask what the current deadline is before signing any agreement with the IRS, because signing can restart the clock or give the agency more time than it would otherwise have.
What records to keep and for how long
The safest approach is to keep tax records for at least six years. This includes receipts, invoices, bank statements, cancelled checks, and documentation for all deductions and income reported on your return. If you are self-employed or own a business, keep records even longer — seven years is standard for business records because the IRS sometimes looks further back when examining business returns.
For returns involving real estate, investments, or retirement accounts, consider keeping records indefinitely. The IRS can sometimes challenge basis calculations or cost adjustments years later, and having original documentation protects you. Digital copies are acceptable as long as they are legible and you can produce them if requested.
If the IRS contacts you about a return from more than three years ago, do not assume the audit is invalid. The agency may have a legitimate reason to look further back. Gather your records and respond promptly, or contact a tax professional if you are unsure whether the IRS has the right to audit that particular year.
What happens if the statute of limitations expires during an audit
If the IRS is auditing your return and the statute of limitations expires before the audit is complete, the agency must stop. It cannot assess additional tax after the deadline passes. However, the IRS may try to get you to sign a consent form extending the deadline, especially if the audit is taking longer than expected.
You have the right to refuse to extend the statute of limitations. If you do, the IRS must wrap up the audit and issue its findings before the deadline. Refusing an extension can sometimes speed up the process, but it can also frustrate the IRS and lead to a more aggressive final information. Consult a tax professional before refusing an extension, because the decision depends on your specific situation.
If you disagree with the IRS's findings after the statute expires, you may still have appeal rights, but those rights are limited. The statute of limitations protects you from new assessments, but it does not erase assessments the IRS already made before the deadline.
Frequently Asked Questions
Can the IRS audit a return I filed five years ago?
Only if the IRS has a reason to look beyond the standard three-year window. That reason could be substantial underreporting of income (25 percent or more), fraud, or an unfiled return. If none of those apply, the statute of limitations has expired and the IRS cannot audit that year.
Does the statute of limitations reset if I file an amended return?
Filing an amended return does not restart the statute of limitations on the original return. However, if you amend a return to report additional income or claim a larger deduction, the IRS may have three years from the amended return's filing date to audit that amendment specifically. The original return's deadline remains unchanged.
What if I owe back taxes from years the IRS can no longer audit?
If you voluntarily file an amended return or pay taxes you owe after the statute expires, you can do so. The IRS will accept the payment. However, you cannot be forced to pay taxes for years outside the statute of limitations unless fraud or an unfiled return applies to those years.
Does the statute of limitations apply to penalties and interest?
Penalties and interest follow the same statute of limitations as the underlying tax. If the IRS cannot audit the year, it generally cannot assess new penalties for that year either. However, penalties and interest on assessments made before the deadline continue to accrue indefinitely until paid.
How do I know if the IRS is auditing me for fraud versus a routine issue?
The IRS does not always announce fraud allegations upfront. If you receive an audit notice for a year more than three years old, ask the IRS in writing why that year is being examined. The response will indicate whether substantial underreporting, fraud, or another reason applies. If fraud is suspected, the IRS may involve special agents, and you should contact a tax attorney immediately.