Capital gains

A capital gain is the difference between what an investor paid for a position (its adjusted cost base, or ACB) and what the investor received when selling. Gains are "unrealized" while the position is still held and "realized" once the sale is complete. Only realized gains are a taxable event in a non-registered account.

Realized capital losses offset realized capital gains within the same tax year. Net unused losses can be carried back three years or forward indefinitely. Losses cannot offset other kinds of income (like employment income or interest) except to a limited degree in the year of death.

The adjusted cost base matters. Brokerage statements calculate ACB automatically for purchases in one account, but transfers between accounts, return-of-capital distributions, and identical shares held in multiple places (including a spouse's account for same-property rules) can all shift the ACB from what the brokerage shows.