Which Six Years? Counting Back the Way the IRS Does

Once people learn about the six-year rule, the next question is always the same: which six? Six years from when I stopped? Six years from today? Six years from the first IRS letter?

The IRS has an answer, and it is written down. Counting wrong can leave you filing years nobody asked for while missing the one year that triggers the next notice.

The rule: start with the return currently due

The collection manual for delinquent return investigations, IRM 5.1.11, tells Revenue Officers to "calculate the six year period for enforcement by starting with the tax year that is currently due and go back six years." It then gives a chart for individual returns, which I will translate into plain English.

The key question is: what is the most recent return that is already due? For an individual on a calendar year, that depends on whether we have passed the April 15 filing deadline.

The manual adds a note that the start of the calendar year begins the six-year count, but the month determines which prior returns must be addressed. In other words, January 1 does not make the new year's return due. April 15 does.

Applying it to today

This guide was updated in October 2026. Using the IRS method:

• The 2025 return was due April 15, 2026. It is the most recent required return.
• Counting it as year one and going back, the six years are 2025, 2024, 2023, 2022, 2021 and 2020.

That window holds until April 14, 2027. On April 15, 2027, the 2026 return becomes due, the window slides forward, and 2020 drops off the back end. The six years become 2026 through 2021.

Why the count starts with the newest year, not the oldest

People are often surprised that the newest year is year one. The logic is simple. The IRS wants you current first. A taxpayer who files the last six years is in filing compliance going forward. A taxpayer who files six old years and skips the last two is still a non-filer.

This matters for the order you file in, too. It is tempting to start with the oldest year because it feels like "catching up." In most cases the IRS cares most about the recent years, and those years are also where your records are easiest to find.

What about extensions?

If you filed an extension for the most recent year and the extended deadline has not passed, that year is not yet delinquent. The IRS manual on installment agreements treats a return on an approved extension as being in filing compliance (IRM 5.14.1.4.2). Once the extended deadline passes without a return, that year becomes part of the count like any other.

Where people go wrong

Counting from when they stopped filing

If you stopped filing in 2012, the IRS is not normally going to start with 2012 and work forward six years to 2017. That would leave the most recent years unfiled. The count runs backward from today.

Ignoring a year that already has an SFR

Sometimes the IRS has already prepared a substitute for return for a year. That year has an assessment on it. Whether or not it falls inside the six, it needs attention, because the SFR balance is often much higher than the tax you actually owe. Replacing it with an original return is covered in the SFR reconsideration process.

Forgetting the current year

While you are catching up on six old years, the clock keeps running on the current one. If the current year's return comes due while you are working on the back years, file it too. Otherwise you finish the package and you are already one year behind again.

Assuming the count is the same in Examination and Collection

The count method above comes from the collection manual. The examination manual, IRM 4.12.1.3, applies the same six-year policy. In practice the result is usually the same, but the IRS employee assigned to your case controls the request. Read the letter or ask exactly which periods the employee wants.

A worked example

Take a hypothetical taxpayer we will call Maria. She last filed for 2015. It is now October 2026. She has received IRS notices for 2022 and 2023, and the IRS has prepared a substitute for return for 2021.

1. The most recent required return is 2025. Her six-year window is 2020 through 2025.
2. She has unfiled years 2016 through 2025. That is ten years.
3. The IRS will normally enforce 2020 through 2025, which is six returns.
4. The 2021 SFR is inside the window. Her original 2021 return will replace the IRS's numbers through reconsideration.
5. The 2022 and 2023 notices have deadlines. Those returns go to the front of the line.
6. Years 2016 through 2019 are outside the normal window. Whether she files any of them is a separate decision, made with advice. See should you file years older than six.

Maria's filing order would likely be 2023 and 2022 first, then 2021 to replace the SFR, then 2024, 2025, and 2020. Her exact order depends on the deadlines in her letters and whether any year is a refund year.

Why the IRS counts this way

The counting method is not arbitrary. It lines up with how the IRS finds non-filers in the first place. The collection manual explains that delinquency checks for individuals are run against the IRS master file, and that checks using information returns such as Forms W-2 and 1099 are generally run about ten months after the due date of the return (IRM 5.1.11.2.1). Each spring, a new year becomes due. Each year after that, a new batch of potential non-filers is identified.

Because the system works one filing season at a time, the six-year window has to move one filing season at a time too. Anchoring the count to the return currently due keeps the window aligned with the years the IRS is actively matching against third-party data.

It also explains why recent years tend to generate notices first. They are the years the IRS computers have looked at most recently. Older years were looked at too, back when they were recent, but if nothing came of it then, they tend to stay quiet unless a person at the IRS decides to reach back.

Keep a written filing map

Before you prepare a single return, write down every year from the oldest unfiled year to the current one. Next to each year, note four things: whether the IRS shows a return, whether there is an SFR or assessment, whether you have a notice with a deadline, and whether you think it is a refund or balance due year. That one page will drive every decision that follows, and it keeps you from wasting money preparing returns in the wrong order.

The count is a starting point

The six-year window is how the IRS normally works. It is not a ceiling the IRS has to respect. Policy Statement 5-133, at IRM 1.2.1.6.18, lets managers approve enforcement beyond six years, and it lists the factors that make that more likely. Read when the IRS wants more than six years if your case has a long history of non-filing or significant income.

Count the right six. File them accurately. Then deal with what is left. That order saves money and keeps the IRS from writing your returns for you.