How to Calculate a Collection Statute Expiration Date, Step by Step

The collection statute expiration date, or CSED, is the single most important date in most IRS collection cases. After it passes, the IRS cannot collect. The balance does not get forgiven. It expires. Every strategic decision about paying, offering, or waiting depends on knowing that date, and knowing it accurately.

The rule

IRC 6502(a) says that when tax has been timely assessed, it may be collected by levy or court proceeding if begun within 10 years after the assessment. IRM 5.1.19.1.1 puts it plainly: each tax assessment has its own CSED, and the expiration ends the government's right to pursue collection.

Two words in that rule do all the work: assessment and each. The clock starts at assessment, not at the due date. And every assessment has its own clock.

Step 1: find the assessment date

Pull your account transcript for the year. The original assessment of a filed return posts as TC 150. The date next to it is the assessment date (often called the 23C date). If the IRS later assessed more tax, those assessments post as TC 290, TC 300, and similar codes, each with its own date. IRM 5.1.19.2.1 lists the transaction codes that carry their own CSED, including TC 290 and TC 300 for additional tax and several penalty codes.

Step 2: add exactly ten years

The base CSED is the same calendar date ten years after the assessment date. IRM 5.1.19.3 gives an example: tax assessed June 1, 2009 had an original CSED of June 1, 2019.

Step 3: list every tolling event

Certain events suspend the running of the ten years. The clock stops, and the days it was stopped get added to the end. The common ones:

Each has its own guide on this site with worked dates: offers, installment requests, CDP hearings, bankruptcy, and living abroad.

Step 4: count the days the IRS way

The IRM's own example in IRM 5.1.19.3 shows the method. Suspension from May 10, 2014 through November 16, 2015 extended the CSED by 555 days, moving it from June 1, 2019 to December 7, 2020. 555 is the number of days from the start date to the end date. Add that number of days to the old CSED.

Overlaps count once

The same IRM section says overlapping suspensions run concurrently, not cumulatively. If an offer is pending while you are also in a combat zone, the overlapping days are counted once. Merge overlapping periods before you add them up.

Worked example: two tolling events

Use the 2021 return above, base CSED May 23, 2032. Two things happen:

1. An offer in compromise is accepted for processing February 3, 2025 and rejected October 14, 2025. No appeal. Suspension runs from February 3, 2025 through the 30 days after rejection, which ends November 13, 2025.
2. A timely CDP hearing request is received January 12, 2026. The Appeals determination becomes final June 30, 2026, with no court appeal.

Two ordinary collection steps added almost fifteen months to the IRS's collection window. That is not a reason to avoid an offer or a hearing. It is a reason to know the cost before you file.

Step 5: check what the IRS has on file

The IRS records suspensions with transaction codes. IRM 5.1.19.2.2 lists, among others, TC 480 (offer pending), TC 520 with certain closing codes (bankruptcy or litigation), TC 550 (waiver or manual CSED update), and TC 971 with action code 043 (pending installment agreement) or 163 (terminated installment agreement). Your transcript shows these codes and their dates. Compare them to your own records. Errors happen, and they usually run in the IRS's favor.

What the CSED does not do

• It does not stop interest or penalties from accruing until it arrives. Under IRC 6601(g), interest can be collected for as long as the tax can.
• It does not prevent the IRS from keeping levy proceeds from a levy served before the CSED, in some circumstances; IRM 5.1.2.6.4.1 notes that exception.
• It does not apply across the board. A later audit assessment for the same year has its own, later CSED. See multiple assessments.

Why this number drives strategy

If the CSED is close, paying voluntarily toward that year may be money you did not need to spend; see how the IRS applies payments. If an offer would add a year to a clock that has eighteen months left, waiting in a hardship status may be the better math. The background is in Statute of Limitations on IRS Collections, and the firm's CSED guide covers the strategy side.

Worked example: the IRM's overlap case, step by step

IRM 5.1.19.3 includes an example worth walking through, because it shows why overlaps must be merged. A 2008 Form 1040 balance was assessed June 1, 2009, so the original CSED was June 1, 2019. The taxpayer, a reservist, entered a combat zone on May 10, 2014 and left on March 1, 2015. The combat zone suspension ran through March 1, 2015 plus 180 days, which the IRM puts at August 28, 2015. Separately, the taxpayer submitted an offer on April 20, 2015, which was rejected October 17, 2015 and not appealed, so that suspension ran to November 16, 2015.

Counted separately, the combat zone period is 475 days and the offer period is 210 days, a total of 685. That would be wrong. The two periods overlap from April 20 to August 28, 2015. Merged, the suspension runs continuously from May 10, 2014 to November 16, 2015, which is 555 days. Add 555 days to June 1, 2019 and the new CSED is December 7, 2020, which is the date the IRM reaches. Double-counting the overlap would have given the IRS 130 extra days it was not entitled to.

Worked example: a late-filed return

Late filing pushes the whole clock later. Say a 2019 return, originally due in 2020, is not filed until August 2, 2023, and the IRS assesses it on September 18, 2023. The CSED is September 18, 2033. A taxpayer who assumes the 2019 debt expires around 2030 is three years off. The return's due date does not matter for the collection statute. The assessment date does.

The same logic applies to a substitute for return. If the IRS assessed tax under IRC 6020(b) and deficiency procedures, the CSED runs from that assessment, per IRM 5.1.19.3.15. Filing your own return afterward does not restart it unless your return shows more tax, which creates a second assessment with its own CSED.

Common counting mistakes

• Using the tax year or the due date instead of the assessment date.
• Adding overlapping suspensions twice instead of merging them.
• Forgetting the 30 days after an offer or installment agreement rejection.
• Treating an installment agreement in effect as a suspension. It is not.
• Using the date you mailed a request instead of the date the IRS received or accepted it.
• Assuming one CSED per year when the transcript shows several assessments.

When you finish, write the result down in a table: assessment, assessment date, base CSED, each suspension with its start and end dates, merged total, and adjusted CSED. That one page is the foundation for every collection decision that follows, and it is the first thing a representative will ask for.

The bottom line

Find each assessment date, add ten years, add every suspension day once, and check the transcript codes. That is the CSED. Get it wrong by six months and you can make a five-figure mistake in either direction. If your case turns on the date, have it calculated from the transcripts, not from memory.