ACB Calculator — Adjusted Cost Base for Stocks (Canada)

Stop guessing your cost basis. Enter your stock purchases one by one — the calculator applies the CRA's identical properties (weighted average) rule and shows your ACB per share, capital gain, and estimated tax at any selling price.

Why ACB matters

Your adjusted cost base is what you subtract from your selling price to calculate your capital gain. Get it wrong — in either direction — and you either overpay tax or underreport income.

For a single purchase, it's simple: purchase price + commissions. But when you've bought the same stock multiple times at different prices, the CRA's identical properties rule requires you to use a weighted average ACB across all shares. You cannot choose which lot you're selling.

The identical properties rule

When you hold multiple purchases of the same security, every share you hold is considered identical. Each time you buy more shares, the ACB of all your shares is recalculated:

New ACB per share = (Previous total ACB + New purchase cost + Commission) ÷ Total shares held

This calculator handles that math automatically as you add purchase lots.

What goes into the ACB

• Original purchase price per share
• Brokerage commissions paid at purchase (divided across shares)
• Reinvested dividends (DRIP shares have an ACB equal to the amount reinvested)
• Return of capital distributions (these reduce your ACB — not handled by this calculator)
• Stock splits and consolidations (adjust your share count and price accordingly)

What reduces your ACB

Certain distributions reduce the ACB of your shares rather than being taxed immediately:

• Return of capital (ROC) from mutual funds, ETFs, or REITs
• These reduce your ACB per share, increasing the capital gain when you eventually sell

For assets with ROC history, you'll need to manually adjust the ACB per share before entering it here.

Superficial loss rule

If you sell shares at a loss and repurchase the same security within 30 days before or after the sale, the CRA denies the capital loss. The denied loss is added back to the ACB of the repurchased shares instead. This calculator does not track the superficial loss rule — keep this in mind when selling at a loss.

Related tools and guides

• Canadian Capital Gains Tax Calculator
• Capital Loss Planner
• How to Calculate Adjusted Cost Base in Canada
• How Capital Gains Tax Works in Canada (2025)

Disclaimer: For stocks with complex histories (stock splits, return of capital, employee options), manual adjustments may be required. Consult a Canadian tax professional.