What goes into the cost base
For most property, the starting point is the purchase price plus the expenses of acquiring it, such as commissions and legal fees. Money spent on additions and improvements generally increases the cost, while routine maintenance and repairs are current expenses that do not. If you bought in a foreign currency, the cost is converted into Canadian dollars at the exchange rate in effect when you acquired the property.
Keep the cost base separate from the costs of selling. Commissions, advertising and legal fees you pay on the sale are outlays and expenses of disposition. They are subtracted from your proceeds alongside the ACB rather than added to it, so recording them in the wrong place can distort the figure you carry forward.
Averaging for identical shares and units
If you buy the same security at different times, such as shares of one class of a company or units of one mutual fund trust, you generally calculate an average cost per unit after each purchase. A later sale does not change the average, but it reduces the number of units you still hold. Stock splits and consolidations also require the per-share figure to be recalculated.
As an illustration, suppose you buy 100 shares for $1,000 plus a $10 commission, so the ACB is $1,010. You later buy 100 more for $1,400 plus a $10 commission. The total cost is $2,420 for 200 shares, or $12.10 each. If you then sell 50 shares for $800 and pay a $10 commission, the ACB of the shares sold is $605. The gain is $800 less $605 and less $10, which is $185. The 150 shares you keep carry a total ACB of $1,815. These numbers are illustrative only.
Special cases and common mistakes
Personal-use property, such as a boat or furniture, has a minimum cost base of $1,000 for these calculations, and a sale where both cost and proceeds are $1,000 or less produces no reportable gain or loss. Property owned before 1972, and units of mutual fund trusts whose tax slips show a cost base adjustment, need extra steps. A loss denied under the superficial loss rule is usually added to the ACB of the replacement property.
The usual errors are using only the latest purchase price, forgetting reinvested distributions, and relying on a platform’s displayed cost after moving accounts. Crypto-assets follow the same idea, so keep a record of each purchase and how you calculated the cost.
What to discuss with your accountant
Bring purchase confirmations, statements showing commissions, and records of improvements to real estate. For property you inherited, received as a gift or began using differently, the CRA expects you to keep the fair market value on that date.
Ask how the cost base was set for any property that was gifted, inherited or transferred between family members, and how to reconcile your own records with the figures on a brokerage statement.
Sources & editorial notes
Sources checked October 24, 2026. The examples are illustrative and provide general information. Discuss how the guidance applies to your circumstances with your accountant.
- Calculating and reporting your capital gains and lossesCanada Revenue Agency
- Guide T4037, Capital GainsCanada Revenue Agency
Rules and guidance can change. Use the current official source and confirm the treatment for your facts. To flag an error, contact Sora.