Canada › Guides

Adjusted cost base for IBKR trades: a Canadian ACB guide

Updated: 21/10/2026

How to calculate the adjusted cost base in CAD for Interactive Brokers trades, why IBKR's P/L and T5008 differ, and what goes on Schedule 3, with an example.

Your adjusted cost base (ACB) is the average cost of all identical shares you own, in Canadian dollars, including commissions. For each sale in your Interactive Brokers account, the capital gain is the CAD proceeds minus selling costs minus the shares sold times the ACB per share — and for 2025, half of your net capital gain is taxable.

Canada does not use first in, first out. All identical shares you hold in non-registered accounts form one pool with a single average cost. IBKR's realized P/L, by contrast, follows the lot-matching method chosen in your account and is calculated in the trading currency, so it rarely matches the CRA's result.

The T5008 slip is no better as a shortcut. It reports proceeds, and the cost figure, when it is filled in at all, only knows about that one account. If you also hold the same stock at another broker, the pool includes those shares too. You are responsible for the ACB you report, not the broker.

• Convert every purchase to CAD at the exchange rate for the day of the trade, using the Bank of Canada rate or another rate the CRA accepts, applied consistently.
• Add commissions to the cost of each purchase.
• ACB per share = total CAD cost of the pool ÷ number of shares in the pool.
• On a sale: gain or loss = CAD proceeds − selling commission − (shares sold × ACB per share).
• A sale reduces the pool's total cost proportionally, so the ACB per share of the shares you keep stays the same.

You buy 10 shares at US$100 when US$1 = C$1.30, costing C$1,300, then 10 more at US$120 when US$1 = C$1.35, costing C$1,620. The pool is 20 shares costing C$2,920, so the ACB is C$2,920 ÷ 20 = C$146 per share.

You then sell 15 shares at US$130 when US$1 = C$1.37:

• Proceeds: 15 × US$130 = US$1,950 × 1.37 = C$2,671.50
• Cost: 15 × C$146 = C$2,190
• Capital gain: C$2,671.50 − C$2,190 = C$481.50
• Taxable capital gain at 50%: C$240.75

The 5 remaining shares keep an ACB of C$146 each, C$730 in total. Commissions are left out here to keep the arithmetic clear; in real life, add them to the purchase cost and subtract them from the proceeds.

• Further purchases, including reinvested dividends (DRIP), add to the pool.
• Stock splits and consolidations change the number of shares but not the total cost.
• Return of capital distributions reduce the ACB.
• Reinvested capital gains distributions from Canadian ETFs increase it.
• A denied superficial loss is added to the ACB of the shares you bought back.

1. In the IBKR Client Portal, open Performance & Reports, then Statements, and run Annual Activity statements for 2025 and every earlier year in which you bought the shares you sold.
2. For each security, list all buys and sells in date order with quantity, price, commission and currency.
3. Convert each transaction to CAD at that day's rate and keep a running pool of shares and total cost.
4. For each 2025 sale, calculate proceeds, ACB of the shares sold, outlays and the gain or loss.
5. Report each disposition in the publicly traded shares section of Schedule 3: description, number of shares, proceeds, ACB and outlays.
6. Carry 50% of the net gain to line 12700 of your T1. A net capital loss can be carried back three years or forward indefinitely, but only against capital gains.

• Using one year-end exchange rate for every trade instead of the rate on each transaction date.
• Restarting the ACB each year instead of carrying the pool forward from the very first purchase.
• Copying the T5008 cost, or leaving it blank and reporting the full proceeds as gain.
• Including trades from a TFSA or RRSP, which never belong on Schedule 3.
• Forgetting that converting US dollar cash back to Canadian dollars can itself produce a foreign exchange gain or loss; for individuals, only the net amount above C$200 for the year is reported.

The 2025 return was due on April 30, 2026. Filing late with a balance owing costs 5% of that balance plus 1% for each full month late, up to 12 months, with daily compound interest on top. If you already filed using IBKR's figures, you can correct the return through Change my return in CRA My Account.

A wrong cost base is one of the easiest errors for the CRA to question, and an overstated gain is money you simply hand over. Upload your IBKR statements to Brokers.tax and see the ACB of every security in CAD across all your years, with each Schedule 3 figure laid out before you file or fix your return.