If a taxpayer alternates between 2 properties, using each as a residence for successive periods of time, the property that the taxpayer uses a majority of the time during the year ordinarily will be considered the taxpayer's principal residence. In the case of a taxpayer using more than one property as a residence, whether property is used by the taxpayer as the taxpayer's principal residence depends upon all the facts and circumstances. Property used by the taxpayer as the taxpayer's residence does not include personal property that is not a fixture under local law. A property used by the taxpayer as the taxpayer's residence may include a houseboat, a house trailer, or the house or apartment that the taxpayer is entitled to occupy as a tenant-stockholder in a cooperative housing corporation (as those terms are defined in section 216(b)(1) and (2)). Whether property is used by the taxpayer as the taxpayer's residence depends upon all the facts and circumstances. Subject to the other provisions of section 121, a taxpayer may exclude gain only if, during the 5-year period ending on the date of the sale or exchange, the taxpayer owned and used the property as the taxpayer's principal residence for periods aggregating 2 years or more.

Section 121 provides that, under certain circumstances, gross income does not include gain realized on the sale or exchange of property that was owned and used by a taxpayer as the taxpayer's principal residence. § 1.121-1 Exclusion of gain from sale or exchange of a principal residence.

Syncios 6.5.8 reg code