How Far Back Can the IRS Audit? Three, Six and No Limit

How far back can the IRS audit your tax return?

The IRS generally has three years from the date a return was due or was filed, whichever is later, to assess additional tax. As a matter of practice the agency states that it usually includes returns filed within the last three years, adds years when it identifies a substantial error, and rarely goes back more than six.

The governing deadline has a name. The IRS calls it the Assessment Statute Expiration Date, and the page on the time the IRS can assess tax states the default plainly: tax can usually be assessed within three years after the return was due, including extensions, or within three years after a late return was received, whichever of the two is later.

Audit practice is narrower than audit authority, and the two get quoted interchangeably. The IRS audits page states that examinations generally include returns filed within the last three years, that additional years may be added where a substantial error is identified, and that the agency usually does not go back more than the last six years. The same page notes that most examinations cover returns filed within the last two years, because the IRS tries to open them as soon as it can after filing.

The distinction between the two ideas matters when a letter shows up about a year that is four or five years old. That is outside ordinary practice but not necessarily outside the law, because the exceptions below can lengthen the period, and several events can suspend it while it runs.

When does the three year assessment clock start?

It starts on the later of two dates: the day the return was due, including any extension, or the day the IRS received the return. A return filed before the due date is treated as filed on the due date, so filing early does not start the period running any sooner than the statutory deadline does.

The IRS gives two worked examples on its assessment page. A 2021 individual return filed on the due date of April 18, 2022 carries an assessment deadline of April 18, 2025. The same 2021 return filed late on October 31, 2022, after the extended due date of October 17, had an assessment deadline of October 31, 2025. Filing late in that second example pushed the deadline out by more than six months.

The rule that returns filed early are treated as filed on the due date comes from Topic no. 305 on recordkeeping, which states the periods of limitation in one place. Filing in February does not buy an earlier expiration than filing in April does. Filing after the deadline, by contrast, moves the expiration later by exactly as long as the delay.

One more wrinkle sits inside the same rule. An extension moves the due date, so a return placed on extension and filed in September has a later starting point than the same return filed in April. The extension does not shorten the three years, and it does not lengthen them either. It simply moves the event the count begins from.

When does the IRS get six years instead of three?

The period doubles to six years when income that should have been reported was left off, and the omitted amount is more than 25 percent of the gross income shown on the return. Topic no. 305 states a second trigger as well: omitted income attributable to foreign financial assets of more than 5,000 dollars.

Two features of this rule surprise people. The first is that the test is measured against gross income reported on the return, not against the tax that would have been owed on the missing amount. A return showing 80,000 dollars of gross income crosses the threshold once more than 20,000 dollars of reportable income is missing from it, regardless of what the additional tax would have come to.

The second is that the six year rule is about omission rather than about error. Topic no. 305 frames it as income that should have been reported and was not. An overstated deduction is a different kind of mistake, and it is not what this particular exception is written around.

• Omitted income of more than 25 percent of the gross income shown on the return extends the assessment period from three years to six, running from the date the return was filed.
• Omitted income attributable to foreign financial assets of more than 5,000 dollars carries the same six year period under Topic no. 305.
• The comparison is made against gross income stated on the return, which means the threshold moves with the size of the return rather than being a fixed dollar figure.

Unreported income is also the category the IRS is best equipped to spot without an examination at all, because payers file matching information returns. That automated comparison usually surfaces as a CP2000 notice proposing changes, or its earlier cousin the CP2501, rather than as an audit letter.

When is there no time limit on an IRS audit?

Two situations remove the deadline entirely. A false or fraudulent return filed with intent to evade tax can be assessed at any time. So can a year for which no valid return was ever filed, because the three year period never begins running in the first place without a filed return.

The non-filing case is the one worth understanding properly, because the outcome is counterintuitive. The assessment page states that tax can be assessed at any time under the Substitute for Return program where a required return was not voluntarily filed, citing IRC 6020, and that the three year limit for assessment does not begin in that situation.

The same page then states the other half of the rule, which is the part that rarely gets quoted. If a return is later filed for that year, filing it does start the three year period running. An open-ended exposure becomes a period with an end date on it once a return exists.

The fraud exception is narrower than the anxiety around it suggests. The statute is written around a false or fraudulent return filed with intent to evade tax, which is a question of intent rather than of accuracy. An incorrect figure is not the same thing as a fraudulent one, and the full list of exceptions the IRS relies on is set out in IRC 6501.

Can the IRS ask you to extend the audit deadline?

Yes. When an examination is still open as the assessment period approaches its end, the examiner may request a signed consent extending it. Publication 1035 describes fixed date consents made on Form 872, open-ended consents made on Form 872-A, and restricted consents that limit the extension to specific unresolved issues.

Publication 1035, Extending the Tax Assessment Period, sets out how these agreements work. A fixed date consent names a specific expiration date and is used for most examination and appeal activity. An open-ended consent runs for an indefinite length of time, and the publication states that it generally remains open until 90 days after either side sends the prescribed notice ending the agreement.

Signing is not compulsory. The IRS audits page states that a request to extend the statute can be refused, and that the auditor will then be forced to make a determination based on the information already provided. Publication 1035 also notes the IRS position that a taxpayer has the right to request a restricted consent, subject to conditions such as the number of unresolved issues being small enough to make it practical.

There is a reason examiners frame the request as cutting both ways. The same publication explains that an administrative appeal within the IRS cannot be provided unless sufficient time remains on the statute of limitations. An extension therefore keeps the assessment period open for the government and keeps the appeal route open at the same time.

What pauses the assessment clock once it is running?

Issuing a notice of deficiency suspends the three year period. The suspension begins the day after the letter is mailed and ends 60 days after a final Tax Court decision, covering the 90 day response period, or 150 days for a recipient living outside the United States. A bankruptcy filing also suspends the period.

A notice of deficiency, often called a 90 day letter, arrives as a CP3219A or a similar statutory notice. The assessment page states that the recipient has 90 days, or 150 days when living outside the United States, to agree with the proposed assessment or to file a petition with the Tax Court before the IRS can assess the amount. The clock stops for that period and restarts after the matter concludes.

The page also states what happens where no petition is filed within that period. The IRS assesses the amount shown in the notice of deficiency, and the balance becomes payable along with applicable penalties and interest. That assessment is the event the collection clock discussed below begins from.

• A notice of deficiency suspends the assessment period starting the day after the letter is mailed and ending 60 days after a final Tax Court decision.
• A bankruptcy petition suspends the period where a notice of deficiency is issued shortly before, on the same day as, or after the petition, and before the automatic stay terminates.
• The statutory provisions the IRS lists for these rules are IRC 6501, IRC 6503(a), IRC 6213(f) and IRC 6020(b).

Suspensions are the reason a year can still be open long after a simple three year count would suggest otherwise. Time spent inside a deficiency proceeding or a bankruptcy does not count against the government the way ordinary calendar time does.

Is the audit deadline the same as the collection deadline?

No, and treating them as one deadline is the most common mistake made on this topic. Assessment is the act of formally recording a liability, and it is generally limited to three years. Collection is the pursuit of a balance already assessed, and it runs for up to ten years from the assessment date.

Publication 594, The IRS Collection Process, states the collection period directly: the IRS can attempt to collect taxes up to ten years from the date they were assessed. That is a separate deadline with a separate starting event, and it does not begin until an assessment exists.

Sequencing the two clocks explains a pattern that otherwise looks contradictory. A return filed in 2020 can be examined into 2023 under the ordinary rule, produce an assessment in 2023, and then carry a collection period reaching into 2033. Nothing improper has happened, and no single deadline has been stretched. Two consecutive deadlines have simply run one after the other.

The Taxpayer Bill of Rights treats knowing both of these as an entitlement in its own right. The right to finality is described there as the right to know the maximum amount of time available to challenge an IRS position, the maximum amount of time the IRS has to audit a particular tax year or collect a tax debt, and when an audit has finished.

How long should tax records be kept?

The IRS ties record retention to the period of limitations for the return the records support. The baseline is three years. It becomes six years where more than 25 percent of gross income was omitted, seven years for a worthless securities or bad debt claim, and indefinite where no return was filed or a fraudulent one was.

The page on how long records should be kept sets out the retention periods as a direct function of the limitation periods. Records supporting an item of income, deduction or credit are kept until the period of limitations for that return runs out, which means the retention answer changes with which window applies.

Property records follow a different logic worth noting separately. Topic no. 305 states that records relating to property are kept until the period of limitations expires for the year in which the property is disposed of in a taxable disposition, because those records establish the basis used to figure gain or loss. A holding period of twenty years therefore implies a records period of roughly the same length plus the limitation window.

One practical consequence follows from the table. Because the six year and indefinite windows attach to circumstances rather than to a choice, a three year retention habit lines up with the ordinary case and with nothing else.

What happens when a notice arrives about an older tax year?

A letter about a prior year is not automatically outside the window, because the deadline depends on when that return was filed and on whether an exception or suspension applies. The code printed on the notice identifies which process opened, ranging from automated document matching to a formal statutory notice.

The IRS states that examinations are opened by mail and are never initiated by telephone. The letter itself carries the code that identifies the process, and the codes describe quite different situations even though they all cause the same jolt on arrival.

• CP2000 proposes changes from automated matching of information returns against the filed return, which is not an examination in the formal sense.
• CP75 requests supporting documentation, most often where a credit is being verified.
• Letter 566 opens a correspondence examination and asks for records supporting specific items.
• Letter 525 transmits examination findings and the proposed adjustment for review.
• CP3219A is the statutory notice of deficiency carrying the Tax Court petition period described above.
• CP05 reports that a return is being reviewed before a refund is released, which is a hold rather than an adjustment.

Understanding what triggers selection in the first place is a separate question from how many years are exposed, and it is covered in the companion piece on what actually raises audit risk. The Taxpayer Advocate Service page on audits and examinations covers the process from the taxpayer side, and the IRS notes that Publication 1, Your Rights as a Taxpayer, sets out the examination and appeal processes along with the right to representation.