Adjusted Cost Base (ACB)

Adjusted Cost Base (ACB) is the running cost, in Canadian dollars, of a property you hold — the figure the Canada Revenue Agency (CRA) requires you to subtract from your proceeds when you calculate a capital gain or loss on disposition. For Bitcoin and other cryptocurrencies, ACB is the foundation of nearly every tax calculation a Canadian miner or holder makes: get it right and filings are mechanical; get it wrong and every downstream number is wrong with it. This entry is general information, not tax advice — confirm your own situation with a qualified Canadian tax professional.

The average cost method

Because units of Bitcoin are identical property, the CRA does not let you pick which coins you sold. Instead you pool them and track a single average ACB per unit. If you buy 1 BTC at CAD $40,000 and later another at CAD $60,000, your pool is CAD $100,000 for 2 BTC — an ACB of CAD $50,000 per coin. Every new acquisition re-averages the pool; every disposition removes coins at the current average. Acquisition costs are part of the base: exchange commissions and fees paid to acquire the asset are added to ACB, which slightly reduces the eventual gain. Note the pooling applies per kind of property — bitcoin averages with bitcoin, not with other assets.

What counts as a disposition

The ACB machinery activates more often than sellers expect. Selling for dollars is a disposition, but so is swapping one cryptocurrency for another, spending coins on goods or services, and gifting them — each is measured against the pool's average ACB at that moment, using fair market value in CAD. A common and expensive surprise is the crypto-to-crypto trade: no dollars changed hands, but a taxable event still occurred and the ACB pool of both assets moved.

Why miners must track it carefully

Mining adds a wrinkle. When you receive mined coins, their fair market value at receipt is generally income — see mining as business income — and that same value becomes the ACB of those coins going forward. When you later sell, you compare proceeds to that ACB to find the gain or loss; without a recorded receipt value, you cannot support either number. Sloppy ACB records are the most common reason Canadian crypto filers get reassessed, because the CRA can challenge any cost figure you cannot document. The fix is boring and effective: keep dated records of every acquisition, receipt, fee, and disposition, valued in CAD at the time, and reconcile the pool at least yearly rather than at filing panic.

Where ACB flows next

ACB feeds directly into your capital gains calculation on every disposition. It also interacts with loss rules: a loss denied under the superficial loss rule — selling at a loss and re-acquiring identical property within the restricted window — is not lost outright but added back to the ACB of the re-acquired coins, deferring the deduction rather than erasing it. For a sovereign holder, disciplined ACB tracking is simply part of self-custody: the same care you give your keys, applied to your paper trail.

Tooling helps, but only as far as its inputs. Crypto tax software can automate the pooled-average arithmetic across thousands of rows, yet it inherits every gap in your exchange exports and wallet histories — a missing transfer between your own wallets can be misread as a disposition, silently corrupting the pool. The professional habit is to reconcile the software's closing ACB against your own running record each year and investigate any drift immediately, while the transactions are still fresh enough to explain. Miners with frequent small payouts feel this most: hundreds of receipts per year, each needing a CAD value at its timestamp, is exactly the workload where a disciplined system beats a heroic springtime reconstruction.