Most people think the IRS can come after them forever. For most returns, it cannot. Congress gave the IRS a fixed window to assess additional tax, and for the typical return that window is three years. When it closes, it closes. The IRS cannot send a bill for more tax on that year, and it cannot sue you for it either.

That window is called the assessment statute of limitations. Inside the IRS it goes by its initials, ASED, for Assessment Statute Expiration Date. It is the first clock that matters in any audit, any notice proposing more tax and any decision about whether to answer a letter or sign a form. This guide covers the basic rule, what starts the clock and the traps that keep it from starting at all.

The rule in one sentence

Section 6501(a) of the Internal Revenue Code says the amount of any tax shall be assessed within 3 years after the return was filed, whether or not the return was filed on or after the date prescribed. It also says no court proceeding to collect the tax without an assessment can begin after that period ends.

Two words in that sentence do most of the work: assessed and filed. An assessment is the formal recording of the liability on the IRS books. It is not an audit, not a letter and not a proposed adjustment. The IRS can examine your return in month 35, but if it has not assessed the extra tax by the end of month 36, and nothing has paused or extended the clock, the extra tax is gone.

The other word, filed, decides when the clock starts. That is where most of the mistakes happen.

What counts as filing

The clock does not start until the IRS has a valid return. The Internal Revenue Manual, at IRM 25.6.1.6.14, lists the criteria the IRS applies. The document must have enough data to calculate the tax. It must purport to be a return, with a name, address and taxpayer identification number. It must be an honest and reasonable attempt to satisfy the tax law. And it must be signed under penalties of perjury.

That last point catches people. The same IRM provision says that if a return is received unsigned, the assessment statute does not start until a signed return is received. An unsigned return is not a return for limitations purposes, no matter how accurate the numbers are.

Where you send it matters too. Under IRM 25.6.1.6.15, a document is generally filed on the date it is received at the place the IRS designates for filing. A return handed to the wrong office is not filed until it reaches the right one. If you mail the return, the timely mailing rule in IRC 7502 can treat the postmark date as the filing date, which I cover in the guide to the timely mailing rule.

Early returns, late returns and extended returns

The start date depends on when you file relative to the due date. There are three situations, and each works differently.

  • Early return. Under IRC 6501(b)(1), a return filed before its due date is treated as filed on the due date. If you file your individual return in February, the clock still starts on the April due date. You do not gain anything by filing early, at least as far as this statute is concerned.
  • Late return. Section 6501(a) says the three years run from filing whether or not the return was filed on time. A return filed two years late starts its own three-year clock on the day it is filed. The IRS does not get extra time because you were late, but the clock does not start until you file.
  • Return filed during an extension. IRM 25.6.1.6.15 says an extended due date is not treated like the regular due date. If you have an extension to October and file in July, the return is treated as filed in July, the date it was received, not on the extended due date. The early-return rule only reaches back to the original due date.

Employment tax returns follow their own rule. Quarterly payroll returns filed during a year are treated as filed on April 15 of the following year under IRC 6501(b)(2). That rule gets its own guide on employment tax statutes.

What the IRS has to do before the three years end

For income, estate and gift taxes and certain excise taxes, the IRS cannot simply post an assessment when it decides you owe more. It must first mail a notice of deficiency, the letter often called a 90-day letter, and wait for the period to petition the Tax Court to run. Mailing that notice before the assessment deadline suspends the clock under IRC 6503(a). The IRS does not need to finish the case in three years. It needs to mail a valid notice in three years.

That is why the IRS starts asking for more time as the deadline approaches. If an audit is still open in year three, the examiner has two choices: mail a notice of deficiency based on what the file shows, or ask you to sign a consent extending the deadline. I explain the consent in detail in the guide to Form 872 and the notice in the guide to how a notice of deficiency stops the clock.

The exceptions that swallow the rule

Section 6501(a) opens with the words except as otherwise provided in this section. The rest of section 6501 is a list of exceptions, and some of them are big.

  • Substantial omission. If you leave out more than 25 percent of the gross income stated on the return, the period becomes six years under IRC 6501(e). See the guide to the six-year rule.
  • No return. If no return is filed, IRC 6501(c)(3) lets the IRS assess at any time. See unfiled returns and the open statute.
  • Fraud. A false or fraudulent return with intent to evade tax can be assessed at any time under IRC 6501(c)(1). See the fraud exception.
  • Consent. You and the IRS can agree in writing to extend the period under IRC 6501(c)(4).
  • Unreported foreign information. Certain international information returns that are never filed keep the statute open under IRC 6501(c)(8). See the guide on foreign information returns.

There are more, including special rules for amended returns showing more tax and for listed transactions. The point is not to memorize them. The point is that three years is the starting assumption, and the first job in any case is to rule the exceptions in or out.

Why this date matters to you

The assessment deadline is leverage. When an examiner is running out of time, the IRS has to make decisions. When the deadline has already passed, the IRS has no decision to make, because the year is closed to additional assessment.

It also tells you what not to sign. People sign extension forms because a friendly examiner asks them to, without knowing they had the right to refuse or to limit the extension. They answer letters on years that were already closed and volunteer information that changes nothing except their stress level. Knowing the date first prevents both mistakes.

And it ties into the other two clocks. The date of assessment starts the ten-year collection statute. The date of filing starts the three-year window for a refund claim. One filing date, three consequences.

How to find your date

Do not guess from memory. Your IRS account transcript shows the date the IRS recorded your return as received and the dates of any assessments. From the received date, apply the early-return rule if the return came in before the due date, and then look for anything that changes the period: a consent you signed, a notice of deficiency, an omission large enough to trigger six years.

If the transcript shows a return the IRS prepared for you, sometimes called a substitute for return, be careful. Under IRC 6501(b)(3), a return the IRS executes under its section 6020(b) authority does not start the assessment clock at all. Only your own valid return does that.

The general overview of all three federal tax clocks is in the library article on the three IRS statutes of limitations. This guide is the deeper look at the first one.

The bottom line

Three years from filing is the default. The clock starts on the due date for early returns, on the received date for late and extended returns, and not at all until a signed, valid return reaches the right place. Everything else in the assessment world is an exception to that sentence.

Know your date before you answer the IRS. It is the cheapest protection in tax law.