The Statute of Limitations on Assessment for US taxes is primarily enforced by the Internal Revenue Service (IRS). The length of this period varies significantly based on your filing status.

Generally, there are four main scenarios:

1. General Case: 3 Years If you file on time and report honestly, the IRS assessment period is typically 3 years from the tax return deadline or the actual filing date, whichever is later. Once this 3-year window expires, the IRS generally cannot demand back taxes or conduct an audit.
2. Underreporting Income by More Than 25%: 6 Years (IRC §6501(e)(1)(A)) If you omit more than 25% of your gross income on your tax return, or fail to report more than $5,000 of specific foreign income (from foreign financial assets), the assessment period is automatically extended to 6 years.
3. Indefinite (No Expiration Date) In extreme cases, the assessment period remains permanently open, and the IRS can take action at any time:
• Non-filer: If you fail to file a tax return, the statute of limitations clock never starts.
• Tax Fraud: If you willfully file a false return to evade taxes, the IRS has permanent recourse.
4. Collection Period: 10 Years This is often confused with the assessment period. Once the IRS completes the Assessment (determining exactly how much tax you owe), they have 10 years to collect the payment. This is known as the Collection Statute Expiration Date (CSED).

Summary Table: US Tax Statutes