Crypto ACB and Record Keeping in Canada: Getting the Cost Base Right

Almost every crypto tax problem I see in Canada traces back to the same root cause. Not aggressive positions, not exotic protocols: a cost base that was never tracked properly, reconstructed years later from incomplete exchange exports.

Adjusted cost base is unglamorous and it is the foundation everything else rests on. Get it right as you go and your reporting is arithmetic. Get it wrong and you are rebuilding history from CSV files that no longer exist.

Canada uses average cost, not FIFO

This is the single most important difference from US crypto content, and it trips up a lot of Canadians reading American guides.

The CRA treats crypto of the same type as identical property. Under the identical properties rules you calculate a single pooled adjusted cost base across all of your holdings of that asset, and every disposition uses the average.

You do not choose which coins you sold. You cannot select the highest-cost lot to minimise a gain. There is one pool per asset, and it moves as you buy.

An illustration:

• Buy 1 BTC at $40,000. Pool: 1 BTC, ACB $40,000. Average $40,000.
• Buy 1 BTC at $60,000. Pool: 2 BTC, ACB $100,000. Average $50,000.
• Sell 1 BTC for $70,000. Cost base used is $50,000. Gain $20,000.
• Pool after: 1 BTC, ACB $50,000.

Under FIFO the gain would have been $30,000. Under specific identification it could have been $10,000. In Canada it is $20,000, and there is no election available.

Bitcoin held on three different exchanges is one pool. Not three. The pool follows the asset, not the venue, which is why per-exchange reports almost never produce a correct Canadian ACB on their own.

What adjusts the cost base

Your ACB increases by:

• The purchase price of each acquisition
• Transaction fees and commissions on acquisition
• The fair market value of crypto received as income; mining, staking and similar receipts enter the pool at the value included in your income

Your ACB decreases by:

• The proportionate cost base of each disposition

Fees are the most commonly missed adjustment. Trading fees on acquisition add to your cost base. Fees on disposition reduce your proceeds. Across a few hundred trades this is not trivial, and it is money you are entitled to and routinely leave on the table.

The CRA’s general treatment is in adjusted cost base.

What is a disposition: a longer list than people expect

A disposition is not only selling for Canadian dollars. It includes:

• Crypto-to-crypto trades. Swapping ETH for SOL is a disposition of ETH at fair market value. This is the one people forget, and in an active year it can generate substantial gains with no fiat ever received.
• Spending crypto on goods or services.
• Gifting crypto to another person.
• Converting to a stablecoin. A stablecoin is property, not currency. Moving to USDC is a disposition.

Transferring between your own wallets is not a disposition. No change in beneficial ownership, no gain or loss. But the network fee paid to make the transfer is a real cost, and how it is treated depends on the circumstances: keep the record either way.

Every disposition needs a Canadian-dollar value at the time it happened. For crypto-to-crypto trades that means valuing the asset received, using a consistent and reasonable source, applied the same way throughout the year.

The superficial loss rule applies

If you sell at a loss and you, or an affiliated person, including your spouse or a corporation you control: acquire the same property within 30 days before or after the sale, and still hold it at the end of that window, the loss is denied. It is added to the ACB of the repurchased property instead.

The CRA’s explanation is under superficial losses.

Crypto markets make this remarkably easy to trigger accidentally: a loss realised on Monday and a dip bought on Wednesday is a superficial loss even though nothing about it felt like a wash trade. The planning implications are covered in tax loss harvesting for crypto.

Capital or business income?

The pooled-ACB machinery above assumes your activity is on capital account. If your trading amounts to carrying on a business, gains are fully taxable as business income rather than half-taxable as capital gains, and the analysis changes throughout.

The CRA weighs factors including frequency of transactions, period of ownership, knowledge of the market, time spent, financing, and the nature of the assets. There is no bright line and no volume threshold that settles it.

Mining is typically business income. High-frequency trading often is. Buying and holding generally is not. The cryptocurrency guide sets out the CRA’s approach, and the specific treatment of mining is covered in crypto mining tax in Canada.

Be consistent. Reporting as capital in a gain year and business in a loss year is a position that invites exactly the scrutiny described in CRA audit triggers.

What records to keep

Per transaction:

• Date
• Type; buy, sell, trade, transfer, income
• Asset and quantity
• Value in Canadian dollars at the time
• Fees
• Counterparty or exchange
• Wallet addresses involved

Keep them for six years after the end of the tax year they relate to, per keeping records.

Three practical points that matter more than they look: Export your history from every exchange, now, and store it yourself. Exchanges delist assets, change export formats, restrict historical data, and occasionally cease operating. Your 2019 trade history is your responsibility, and it is not recoverable from a platform that no longer exists.

Reconcile at least annually. Software output that does not tie to your actual wallet balances is telling you something is missing: usually an unrecorded transfer or a forgotten wallet.

Treat crypto tax software as a first draft. These tools are genuinely useful and they consistently misclassify DeFi interactions, unmatched transfers, and anything unusual. Review the output rather than filing it.

Assets you no longer control

Lost keys or an inaccessible wallet do not automatically create a deductible loss, because there has been no disposition. The position is fact-specific and the evidentiary burden is real.

Exchange collapses are similar. Depending on circumstances a claim may arise when the loss becomes established rather than when the platform failed, and the analysis can differ between a capital loss and a bad debt.

Both situations are worth advice rather than a self-assessment. The amounts tend to be large and the rules are not intuitive.

Where to start if your records are already a mess

Do not attempt to reconstruct everything at once.

1. List every venue you have ever used: exchanges, wallets, hardware devices, DeFi protocols, anything.
2. Export whatever history is still available from each, immediately, before it stops being available.
3. Work backwards from your earliest acquisition, since ACB compounds forward and an error in year one propagates through every year after it.
4. Document your assumptions where data is genuinely gone. A reasonable, consistently applied, documented estimate is a defensible position. An undocumented guess is not.
5. Fix the process going forward so this is the last time.

If the gap is large or spans several years, the Voluntary Disclosures Program may be relevant, but only before the CRA contacts you about it.

Crypto reporting is not conceptually difficult. It is a bookkeeping problem that people postpone until it becomes an archaeology problem. If yours has reached that stage, it is worth dealing with deliberately.