Guide

Canadian capital gains on stocks: the cost base nobody keeps

Questrade, Wealthsimple, Interactive Brokers, a bank brokerage — your T5008 reports proceeds, and often reports cost as blank or wrong. The adjusted cost base is yours to track, and it is the figure the whole calculation rests on.

One averaged cost base, recalculated on every purchase

Canada averages. Every identical property — the same shares of the same company, across every account you hold them in — forms one adjusted cost base, and it is recalculated each time you buy. There are no parcels and no holding period: a week and a decade are taxed identically.

Because it is an average across accounts, a purchase in one account changes the cost base of shares sitting in another. No single broker slip can show that, which is why the ACB is the figure people most often get wrong and the one the Canada Revenue Agency expects you to have.

One half of the gain is taxable

The taxable capital gain is one half of the actual gain, added to your income and taxed at your marginal rate. Half of a capital loss is an allowable capital loss, which offsets taxable capital gains — not ordinary income.

Worth knowing if you read older commentary: an increase in the inclusion rate to two thirds was announced, deferred, and then cancelled in March 2025 without ever being enacted. The rate is one half.

The superficial loss rule, and who counts as you

Sell at a loss and buy the same property back within 30 days either side, and if it is still held at the end of that window, the loss is denied — it is added to the cost base of what you bought back instead.

The part that catches people is who counts. The repurchase can be by an affiliated person: a spouse or common-law partner, a corporation you control, or your own RRSP or TFSA. Selling at a loss in a taxable account and buying back inside a TFSA denies the loss. No broker export shows a spouse's account or a registered plan, so this is a question that has to be asked rather than assumed.

Daybook keeps the adjusted cost base as a running average across every account you load, applies the one-half inclusion, and flags superficial losses with the still-held test — then asks about affiliated accounts rather than assuming there are none, because it cannot see them. Working papers come out as a PDF. Nothing is uploaded.

See what Daybook does →

Free to download. Runs on your computer. Reads Interactive Brokers, Questrade and more.

Not tax advice. General information about how some Canadian tax rules apply to investing, not advice about your circumstances and not a substitute for the CRA or a qualified adviser. Check the current rules at canada.ca or with your accountant before you file.

Daybook · Guides: Australia · eToro · United States · United Kingdom · New Zealand · Terms, privacy and refunds