The IRS Statute of Limitations Explained: CSED, ASED, and Why Timing Matters

Every IRS tax debt has an expiration date. Every IRS audit window has a closing deadline. Understanding these statutes of limitations — and the circumstances that can extend them — is one of the most important pieces of knowledge a taxpayer can have. At The Law Office of Pietro Canestrelli, we use statute analysis as a foundational tool in every tax resolution strategy we develop for clients across Temecula, San Diego, Riverside, San Bernardino, and throughout California.

The Two Key Statutes

The IRS operates under two primary statutes of limitations that every taxpayer should understand:

• CSED — Collection Statute Expiration Date: The deadline for the IRS to collect a tax debt (generally 10 years from assessment)
• ASED — Assessment Statute Expiration Date: The deadline for the IRS to assess additional tax (generally 3 years from the filing date or due date, whichever is later)

CSED: The 10-Year Collection Clock

Under IRC Section 6502, the IRS generally has 10 years from the date of assessment to collect a tax debt. After the CSED expires, the debt is legally uncollectible — the IRS must write it off, release any federal tax liens, and stop all collection activity.

The “date of assessment” is typically:

• The date the IRS processes your return showing a balance due, or
• The date the IRS finalizes an audit adjustment adding additional tax, or
• The date a substitute for return (SFR) assessment is made when you failed to file

Important: each tax year has its own separate CSED. If you owe taxes for 2018, 2019, and 2020, each year has its own 10-year clock running independently.

What Tolls (Pauses) the CSED

Several events can toll the CSED, effectively pausing the 10-year clock:

• Offer in Compromise (OIC): The clock pauses while the OIC is pending, plus 30 days after rejection or acceptance
• Bankruptcy: The clock pauses during the automatic stay, plus 6 months after the stay is lifted
• Collection Due Process (CDP) hearing: The clock pauses while the hearing and any Tax Court petition are pending
• Taxpayer Assistance Order (TAO): A Taxpayer Advocate case pauses the clock
• Time outside the United States: If you’re abroad for more than 6 consecutive months, the clock pauses
• Installment agreement requests: The clock pauses while the IRS processes your installment agreement request, plus 30 days
• Military service in a combat zone: The clock pauses for the duration of service plus 180 days

Understanding what tolls the clock is critical to resolution strategy. Filing an Offer in Compromise, for example, pauses the CSED — which means if the OIC is rejected after a year of processing, you’ve added a year to the IRS’s collection window. A tax attorney must evaluate the CSED impact before recommending any resolution approach.

Can You Voluntarily Extend the CSED?

The IRS sometimes asks taxpayers to sign Form 900 (Tax Collection Waiver), voluntarily extending the CSED. This typically happens during installment agreement negotiations or OIC processing when the statute is close to expiring.

You are not required to sign Form 900. Refusing to sign may mean the IRS denies your installment agreement or takes faster enforcement action — but it preserves your statute. This is a decision that should always involve counsel.

ASED: The 3-Year Audit Window

Under IRC Section 6501, the IRS generally has 3 years from the later of the date you filed your return or the due date to assess additional tax. After the ASED expires, the IRS cannot audit you for that year or add tax to your account (with important exceptions).

For example:

• If you filed your 2024 return on April 15, 2025: the ASED expires April 15, 2028
• If you filed early (February 15, 2025): the ASED is still measured from the due date (April 15, 2025) → expires April 15, 2028
• If you filed on extension (October 15, 2025): the ASED expires October 15, 2028

Exceptions That Extend the ASED

Several exceptions significantly extend the 3-year window:

• 25% gross income omission: If you omit more than 25% of your gross income from your return, the ASED extends to 6 years
• Fraud: If the IRS proves fraud with intent to evade tax, there is no statute of limitations — the IRS can audit you for that year indefinitely
• No return filed: If you never file a return, the ASED never begins — the IRS can assess tax at any time. This is one of the most compelling reasons to file delinquent returns. See our guide on unfiled tax returns.
• ERC claims: Under the OBBBA, the ASED for Employee Retention Credit claims has been extended to 6 years from the date of the ERC claim — a critical consideration for businesses that received ERC refunds. See our ERTC audit page.
• Foreign income (Form 8938/FBAR): If you fail to report more than $5,000 of income attributable to specified foreign financial assets, the ASED extends to 6 years
• Consent to extend (Form 872): The IRS may request that you sign Form 872 or 872-A, voluntarily extending the ASED. This commonly happens during audits that are taking longer than expected.

How Statutes Affect Your Tax Resolution Strategy

Understanding both the CSED and ASED is essential to developing an effective tax resolution strategy:

When the CSED Is Close to Expiring

If your CSED is within 3-4 years of expiration and your tax debt is significant, the best strategy may be to request Currently Not Collectible (CNC) status and let the clock run. CNC doesn’t toll the CSED — unlike an OIC or installment agreement request. A tax debt resolution plan that accounts for the CSED timeline can save tens of thousands of dollars.

When the ASED Is Close to Expiring

If the IRS contacts you for an audit and the ASED is about to expire, the IRS may ask you to sign Form 872 to extend the statute. You have the right to refuse — but the IRS may respond by issuing a rapid assessment based on whatever information it has, which could be less favorable than a complete audit would produce. This is a negotiation, and having representation matters.

Multiple Years with Different CSEDs

When you owe taxes for multiple years, each year has its own CSED. In a resolution strategy, this means some years may expire sooner than others — and it may make sense to focus payment or settlement efforts on years with longer-remaining CSEDs while letting shorter-CSED years approach expiration.

How to Determine Your CSED

Your CSED is not printed on IRS notices. To determine your CSED for each tax year, you (or your representative) can:

• Request your IRS account transcript (shows the assessment date for each year)
• File a Freedom of Information Act (FOIA) request for your complete account records
• Have a tax attorney or enrolled agent access your IRS records through e-Services or Practitioner Priority Service

The calculation requires identifying the original assessment date, then adding 10 years, and then adjusting for any tolling events. This analysis can be complex — especially for taxpayers who have had installment agreements, pending OICs, CDP hearings, or time abroad.

Get a Professional Statute Analysis

At The Law Office of Pietro Canestrelli, we perform comprehensive statute analysis for every client with outstanding IRS debt. Knowing exactly when each year’s CSED expires — and which resolution strategies will toll it versus preserve it — is the foundation of an effective tax resolution plan.

We serve taxpayers across Temecula, San Diego, Riverside, San Bernardino, and throughout California and the United States. Whether you’re deciding between an OIC and CNC status, evaluating whether to sign a Form 900, or simply need to understand how much time the IRS has left to collect, contact our office for a case review.