There are two basic statutes of limitation.
First is the statute of limitations, which provides that the IRS has three years to assess an additional tax due.
For example, for a taxpayer who filed a 2012 tax return on April 15, 2013, the IRS has until April 15, 2016, to assess an additional tax.
This rule has two major exceptions. The three-year statute is extended to six years in a case where the taxpayer has omitted more than 25% of gross income.
Second, there is no statute of limitation in cases where no return has been filed, or where the taxpayer has filed a fraudulent return.
These two exceptions permit the IRS to assess an additional tax at any time.
