How is the partial principal residence exemption calculated when I did not live there every year?

When a property qualifies as your principal residence for only some of the years you owned it — for example, because you rented it out for part of your ownership or owned two properties simultaneously — only a portion of the capital gain is sheltered from tax.

The formula used under the federal Income Tax Act is: the gain is multiplied by a fraction, where the numerator is (the number of years designated plus one) and the denominator is the total number of years of ownership. The addition of "one" in the numerator is called the "one-plus rule" and is designed to relieve double taxation when you sell two properties in the same year.

For example, if you owned a property for 10 years, designate it for 8 years, the sheltered fraction is 9/10, meaning 9/10 of the gain is exempt and 1/10 is taxable. The taxable gain then flows through your personal income tax return for the year of sale.

You claim the exemption and report the calculation on Schedule 3. If you also claimed a section 45(2) election (to extend principal residence treatment after a change of use), that affects the number of available designation years. The interaction of these rules can be complex, and a tax professional can model the optimal designation strategy across multiple properties.