Adjusted Cost Base (ACB) Explained: How to Calculate It for Canadian Investments

When you sell an investment, the CRA does not just look at the sale price — it wants to know what you originally paid. That "what you paid" figure is called the adjusted cost base (ACB). Get it right and you pay tax only on your real gain. Get it wrong — typically too low — and you may overpay tax on profit you never actually made.

Understanding adjusted cost base in Canada is essential for anyone who holds investments outside a registered account (TFSA, RRSP, RESP), owns rental property, or holds shares in a private corporation. This article walks through what ACB is, what goes into it, and how to keep track.

What Is the Adjusted Cost Base?

The ACB is the tax cost of an asset — the amount the CRA recognises as your investment in that property for purposes of calculating a capital gain or loss on sale.

The basic idea: if you buy shares for $10,000, your ACB is $10,000. If you later sell for $15,000, your capital gain is $5,000 (before selling expenses). Simple in concept — but the "adjusted" part is where it gets interesting.

What Adjustments Increase the ACB?

The ACB is not always just the purchase price. Several things can increase it:

• Purchase price — the amount you paid for the asset
• Brokerage commissions and transaction fees on the buy side
• Legal fees to acquire the property
• Capital improvements (for real property) — adding a deck, finishing a basement, or replacing a roof adds to the ACB; routine repairs do not
• Reinvested dividends — if you hold a mutual fund or ETF that automatically reinvests distributions, those reinvested amounts add to your ACB (a common source of errors)
• Additional purchases of the same class of shares — see the identical-property rule below

What Adjustments Decrease the ACB?

Certain events reduce the ACB:

• Return of capital (ROC) distributions from funds — these reduce your ACB dollar for dollar, which increases your eventual gain
• Partial dispositions reduce the ACB of the remaining units proportionally

The Identical-Property (Averaging) Rule for Shares

If you buy shares of the same corporation on multiple dates — say, 100 shares in January and 50 more in October — you do not track each lot separately. Instead, the CRA requires you to use an average cost across all identical shares you hold.

Example:

• January: 100 shares × $20 = $2,000
• October: 50 shares × $26 = $1,300
• Total cost: $3,300 for 150 shares → ACB per share: $22

If you later sell 50 shares at $30, your ACB for those 50 shares is 50 × $22 = $1,100, and your capital gain is $1,450 (before selling costs). The averaging rule means you must update your ACB every time you buy more of the same security.

This is the most common ACB tracking error — people use the price they paid on a specific purchase rather than the running average.

ACB for Real Estate

For real property the calculation is more straightforward than for shares, because you typically buy and sell once. Your ACB generally includes:

• Purchase price
• Legal fees on acquisition
• Land transfer taxes paid (not refundable credits)
• Capital improvements over the years of ownership

It does not include mortgage interest, property taxes, or maintenance costs — those may be deductible as rental expenses if the property is income-producing, but they are not part of the ACB.

Keep every receipt for capital improvements. The CRA can ask you to prove your ACB during an audit, and a higher ACB means a lower taxable gain.

ACB for Cryptocurrency

The CRA treats cryptocurrency as property, not currency. The identical-property rule applies: every coin of the same type (e.g., all your Bitcoin) is pooled. Your ACB for each coin is the average cost across all your purchases. Mining income, staking rewards, and airdrops may establish an ACB at the fair market value when received. Crypto ACB tracking is notoriously complex — dedicated software or professional help is strongly recommended.

What Happens If You Do Not Track Your ACB?

If you cannot establish your ACB, the CRA may assume it is zero — meaning you pay tax on the entire proceeds, not just your real gain. This can result in a significant tax bill on money you already spent years ago. Keeping records is not optional; under the Income Tax Act, you are expected to retain records long enough to support any return that could still be reassessed.

How Long Must You Keep ACB Records?

Generally, keep records for at least six years after the last year in which you use them. For long-held property — a rental property owned for 20 years, or shares accumulated over a decade — that means your earliest receipts may need to be kept for decades. Digitise them.

Frequently asked questions