Adjusted Cost Base Calculator

Your adjusted cost base is what the shares you own cost you, commissions included. In Canada, identical shares share one average cost. Buying changes that average. Selling removes the cost of the shares sold and leaves the average where it was.

That is why the cost your broker shows can differ from the one your return needs. The CRA pools identical shares across all your non-registered accounts, so a second broker, a dividend reinvestment plan or a trade in US dollars all feed the same ACB.

Here is the example loaded in the calculator above, worked by hand.

1. You buy 100 shares at $48.20 with a $9.99 commission. The ACB is $4,829.99.
2. You buy 50 more at $52.10. The ACB grows by $2,614.99 to $7,444.98 for 150 shares, which is $49.63 a share.
3. You sell 60 at $61.75. The proceeds are $3,705.00, the ACB of those shares is $2,977.99 and the commission is $9.99, so the capital gain is $717.02. The ACB per share of what you still hold stays at $49.63.

You buy 100 shares on 15 January 2025 at C$20, then another 100 on 15 March at C$30. Each purchase costs C$10 in commission. These are identical shares in your own non-registered accounts, so they share one pool even if you used two brokers.

1. The first purchase adds C$2,010 to ACB. The second adds C$3,010.
2. Total ACB is C$5,020 for 200 shares, or C$25.10 per share. This is a weighted average of the costs, including purchase commissions.
3. On 15 June you sell 80 shares at C$40 with C$10 commission. Proceeds are C$3,200, the ACB sold is 80 × C$25.10 = C$2,008, and selling expenses are C$10. Your capital gain is C$1,182.
4. You still hold 120 shares with C$3,012 of ACB. The cost per share stays C$25.10. With no other gains or losses, the 50% inclusion rate gives C$591 of taxable capital gain, not C$591 of tax.

A Canadian ACB tracker needs the history from every taxable account holding the same security. A broker's average purchase price can miss commissions, earlier purchases at another broker or later cost-base adjustments.

In a separate example with no commissions, buy 100 shares on 15 January 2025 at C$30. Sell all 100 on 1 July at C$20 for a C$1,000 loss. Buy back 50 identical shares in your taxable account on 15 July at C$22 and still hold them on 31 July, 30 days after the sale.

Half the sold shares have been replaced and are still held, so C$500 of the loss is denied. The remaining C$500 capital loss is allowed. The C$1,100 replacement purchase gains C$500 of ACB, giving C$1,600 total ACB, or C$32 per share. The calculator shows the denied amount and a separate ACB addition after the 30-day window.

A superficial loss applies when you or an affiliated person acquire identical shares within 30 days before or after a loss-making sale and still own the replacement shares 30 days after the sale. The CRA denies the loss and adds it to the ACB of the shares you bought back, so the loss is postponed rather than lost. Only the part that matches the shares you bought back is denied.

In the example, the sale on 3 April 2025 loses $231.32 on 40 shares, and 30 shares are bought back 21 days later. So 30/40 of the loss, $173.49, is denied and moves into the ACB of the new shares. The calculator flags it on the sale and shows the ACB addition on its own row.

The rule also looks at purchases by your spouse or common-law partner and inside your own TFSA or RRSP. A buyback in a registered account denies the loss for good, because there is no ACB there to carry it. This calculator checks the trades you enter. The Canadian filing pack checks the accounts included in your report and the spouse or partner holdings you declare.

Each sale is a line on Schedule 3, in the section for publicly traded shares and mutual fund units: the year you bought, the proceeds, the adjusted cost base, your outlays and expenses, and the gain or loss. Half of your net capital gain for the year goes on Schedule 3 line 19900 and T1 line 12700. Losses carried forward from earlier years are claimed separately on T1 line 25300. Your federal and provincial rates then decide the tax.

A sale counts in the year it settles, so one made on 31 December that settles in January belongs to the next year. That is why the calculator asks for settlement dates, and why a US dollar trade uses the exchange rate for its settlement date.

The T5008 slip from your broker shows proceeds, and sometimes a cost. Use the ACB from your own records instead when you hold the same shares in more than one account or switched brokers along the way.