A client hands you a CP2000 dated three years and one day after she filed. Whether that notice is enforceable, and where you can fight it, turns on a handful of dates and doors.
The statute of limitations is a fixed window of time. Inside it, the IRS may assess tax (formally record it as owed) or collect tax it has already assessed, and a taxpayer may claim a refund. Once the window closes, that right is gone for good, which is why you check the dates on a notice before you argue about the tax.
The statute of limitations has three separate clocks, and each one starts on a different event. Keep them apart:
Filing early does not start the assessment clock early. For assessment statute of limitations purposes, a return filed before the due date is treated as filed on the due date. So a 2025 Form 1040 filed February 10, 2026 starts its three-year clock on April 15, 2026, and that clock runs out April 15, 2029.
Common mistakes
- Counting the 25 percent test on taxable income. The IRC 6501(e) test uses the gross income stated on the return, not taxable income. On $180,000 gross income the trigger is $45,000, and overstated deductions never count toward it.
- Treating a CP2000 as a notice of deficiency. A CP2000 gives 30 days to respond, but it carries no Tax Court rights. Only the CP3219A 90-day letter opens the court door, and a petition filed off a CP2000 gets dismissed.
- Letting the 60-day math error window lapse. A math error notice comes with the tax already assessed. After 60 days, the deficiency procedures are gone and only a refund claim remains, so a timely abatement request is the jurisdiction-preserving move.
Bottom line
- Assessment: 3 years, 6 on a greater-than-25-percent gross income omission, unlimited for fraud or no return; collection 10 years from assessment.
- Refund claim: later of 3 years from filing or 2 years from payment, with a matching look-back cap on the recoverable amount.
- Math error notice: 60 days to request abatement or deficiency procedures are lost; CP2000: 30 days, and it is not a notice of deficiency.
- Notice of deficiency: 90 days to petition Tax Court, 150 if addressed abroad, and the period cannot be extended.
Exam shortcut
Read the date first, the issue second. Every stem in this scope hides its answer in a counted interval, so extract the notice date and the contact date before you read the facts. Stem signals to match on sight: "arithmetic error" or "invalid SSN" means math error, 60 days. "Information return does not match" means CP2000, 30 days, no court rights.
The full lesson (about 6,225 words, 42 min read) adds 2 worked examples, all 6 common mistakes, a self-check, free in the app.
Learning objectives
- 6
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