Generally, the statute of limitation for collection expires 10 years after the date the tax was assessed (for tax assessed after November 5, 1990). For tax assessed before November 5, 1990, the statute of limitation for collection is six years. This period may be extended by an agreement between the taxpayer and IRS. In addition, there are numerous circumstances which suspend the running of the statute of limitation for some period of time. For example, the statute of limitation is suspended during the 90-day period after the issuance of a Notice of Deficiency and for an additional 60 days thereafter.
Note: The IRS does not necessarily have to collect the tax during this period, but does have to take collection action (e.g., levy or begin court proceedings) before this time has expired.