If you have net capital losses this year but had gains in up to three previous years, you can apply the losses to the gains to reduce the taxable income in the previous years.
To get to the page, click the link "Net capital loss carryback" on the left. (It is under "Miscellaneous Numbers" in Expert Mode).
The carryback you specified here will be sent to CRA with your return but will not affect your current year return. The CRA will apply the carryback amount to line 253(line 25300 since 2019) of the tax year you specified, then recalculate that return and credit you the difference.
