Capital losses can normally only be used to reduce or eliminate capital gains.  They cannot be used to reduce other income.  If you have capital losses that cannot be used in the current year,  you can carry back the losses to any of the 3 preceding taxation years.  Capital losses can also be carried forward indefinitely.  The only time they can be used to reduce other income is in the year of a taxpayer's death, or the immediately preceding year.  At this time, 1/2 (50%) of the capital loss would be used to reduce other income.   For more on this topic, see the Canada Revenue Agency (CRA) interpretation bulletin IT232R3 - Losses - Their Deductibility in the Loss Year or Other Years (paragraph 30).

Some capital losses may be considered superficial losses, and disallowed.  Also, losses on transfers of shares to an RRSP, TFSA, DPSP or RDSP are not deductible.

Your capital gains and losses must be recorded on the tax return for the year in which the losses occurred.  This applies even when the losses exceed the gains, and cannot be used in the current year.  These losses will then be available to use in a future tax year.  Current year capital gains and losses are reported on Schedule 3 when filing your tax return.  To carry back your current year net capital losses to prior years, you would file form T1A - Request for loss carryback with your tax return.

If you want to revise a previous year's return in which you should have reported capital losses, you would file form T1Adj.  See our article on changing your tax return.

If you have unused net capital losses from previous years, the amount will be shown on your latest assessment notice from CRA.  The amount shown on the assessment notice is the net capital loss, which in recent years has been 1/2 (inclusion rate) of the capital loss.  In order to use some or all of these losses on the current year tax return, you would claim the amount of the net capital loss on line 253 of your tax return.  This amount claimed cannot exceed the amount of taxable capital gains that you are showing on line 127 of your return.

For instance, if your net capital loss with a 2/3 inclusion rate was $2,000, and you are using this to offset taxable capital gains with an inclusion rate of 1/2, the adjusted net capital loss to use would be 

$2,000 ÷ 2/3 x 1/2 = $1,500

The $1,500 would be entered on line 253 of your tax return, as long as your taxable capital gains on line 127 are at least $1,500.

If you have net capital losses carried forward from 1985 and earlier years, special rules apply.  The CRA guide T4037 Capital Gains has a section regarding how to apply your net capital losses of other years to the current tax year, which includes information on pre-1986 losses.