The general rule of the IRS is to audit returns that have been filed in the last three years. Because of this, some taxpayers may breathe a sigh of relief once the three-year period has expired, but the rules regarding the statute of limitations are not quite that simple. There are circumstances where the IRS can go back even further to audit your return or assess additional tax, and the IRS has unlimited time to assess tax in the case of an unfiled return.
IRS Audits for Substantial Errors
If the IRS detects a substantial error on your return, the IRS can wait up to six years after your return was filed to conduct an audit. A substantial error involves an understatement of income of more than 25%, based on the income claimed on the return. Congress has extended this definition of a substantial error to include basis overstatements which result in less capital gains tax being owed after the sale of property. Some of those are discussed below.