Accounts & Tax · Record-keeping
How to track adjusted cost base (ACB)
Your capital gain is only as accurate as your cost base — and ACB quietly drifts every time you buy more, reinvest a distribution, or receive return of capital. This guide shows how to calculate ACB, the adjustments that catch people out, the rule to pool across accounts, and how to avoid overpaying tax when you finally sell.
The short answer
- What it isTotal invested in a security, averaged per share
- Your gainProceeds − ACB when you sell
- ReinvestedRaises ACB — every DRIP purchase counts
- Return of capitalLowers ACB — increasing the eventual gain
What adjusted cost base is
ACB is the total you've invested in a security, used to work out your capital gain when you sell.Your adjusted cost baseThe total you've invested in a security — purchase price plus commissions — adjusted over time. Your capital gain is proceeds minus ACB. is the foundation of every capital gains calculation. When you sell a stock, ETF, or fund, your capital gain is your sale proceeds minus your ACB. Half of that gain is then taxable, as our capital gains tax explained guide describes.
The "adjusted" part is what makes it tricky. ACB isn't just what you originally paid — it changes every time you buy more, reinvest a distribution, or receive return of capital. Track those adjustments and your reported gain is correct; miss them and you'll usually overpay, because your cost base looks lower than it really is.
The average cost rule
When you buy the same security at different prices, ACB is the total invested divided by the total shares — a running average.In Canada you use the average costCanada's required method: every share of the same security shares one blended cost — total dollars invested divided by total units. You can't cherry-pick which lot you sold. method, not first-in-first-out. When you own the same security bought at different prices, your per-share ACB is the total dollars invested divided by the total number of shares. A simple example with one ETF:
- Buy 1: 100 units at $20 + $10 commission = $2,010. ACB = $20.10 per unit.
- Buy 2: 100 units at $30 + $10 commission = $3,010. Total invested $5,020 over 200 units.
- New ACB: $5,020 ÷ 200 = $25.10 per unit.
Selling some units doesn't change the per-share ACB — only the number of units you still hold. If you sold 50 units at $35, your gain would be (35 − 25.10) × 50 = $495. The capital gains calculator handles the gain once you know your ACB.
Reinvested distributions raise your ACB
DRIP purchases and reinvested fund distributions are buys made with already-taxed money — they add to your ACB.This is the single most common ACB mistake. When dividends or fund distributions are automatically reinvestedA DRIP (dividend reinvestment plan) uses your distributions to buy more units automatically. Those purchases add to your ACB even though no new cash left your account. to buy more units — a DRIP — you're buying more shares with money you've already been taxed on. Those purchases add to your ACB, exactly like a cash buy.
Because no cash leaves your bank account, investors routinely forget these. The effect is real: a fund held for years with reinvested distributions can have an ACB far above your original purchase. Omit them and you'll report a gain that's too large and pay tax you don't owe.
Return of capital lowers it
Return of capital isn't taxed when received; it reduces your ACB, which increases the gain you report later.Working the other way is return of capitalA distribution that returns part of your own invested capital rather than income. It's not taxed now; instead it reduces your ACB, increasing your eventual capital gain. (ROC). This is a distribution that isn't income — it's a portion of your own capital handed back to you. ROC isn't taxed when you receive it, but it reduces your ACB, which means a larger capital gain (or smaller loss) when you eventually sell.
Many ETFs and REITs distribute ROC, reported in box 42 of a T3 slip. Like reinvested distributions, it's easy to overlook — and unlike them, ignoring ROC makes your ACB too high, so you'd under-report the gain. Either error can trigger a CRA reassessment, so both adjustments matter.
Know your ACB? Estimate the tax
Once you have an accurate cost base, the calculator works out the capital gains tax on a sale.
Pooling across accounts
Identical securities in different non-registered accounts must be combined into one average cost base.The CRA requires you to poolCombine identical securities held across different non-registered accounts into one shared ACB. You can't keep a separate cost base at each brokerage for the same stock or ETF. identical securities held in different non-registered accounts. If you own the same ETF at two brokerages, you can't keep a separate ACB at each — you combine all the units into a single average cost base. This catches a lot of people who assume each account stands on its own.
Registered accounts are excluded from pooling, because gains in a TFSA or RRSP aren't taxed in the first place. Only your taxable holdings of the same security get averaged together. The same discipline applies to crypto across wallets — see our crypto guide — and to securities at a brokerage, covered in the stocks and ETFs guide.
Tools and record-keeping
T5008 slips often lack an accurate cost base, so keeping your own running ACB record or using tracking software is essential.You can't always rely on your brokerage. A T5008A tax slip listing your securities sales for the year. It often reports proceeds without an accurate cost base, especially when you hold the security at more than one brokerage. slip usually shows your sale proceeds but frequently omits — or misstates — your cost base, especially when you've held the security at more than one institution. The responsibility for an accurate ACB rests with you.
Most Canadian investors keep a running spreadsheet or use a dedicated ACB-tracking website that records every buy, reinvested distribution, and return of capital. Crypto holders generally need specialized software because of the transaction volume. Whatever the tool, the habit is the same: log every adjustment as it happens, so the number is ready when you sell.
Frequently asked questions
Quick answers on tracking adjusted cost base in Canada — the average cost rule, reinvested distributions, return of capital, and pooling.What is adjusted cost base (ACB)?
Adjusted cost base is the total amount you have invested in a security, used to calculate your capital gain when you sell. It is the sum of everything you paid — purchase price plus commissions — adjusted over time for things like reinvested distributions and return of capital. Your capital gain is your sale proceeds minus your ACB. Getting the ACB right is what stops you from over- or under-reporting the gain.
How do I calculate adjusted cost base?
For a single purchase, ACB is simply what you paid plus commission. When you buy more of the same security at different prices, you use the average cost: add up the total dollars invested and divide by the total number of shares. That average per-share cost is your ACB. Each new purchase re-averages it; selling some shares does not change the per-share ACB, only the number of shares you hold.
Do reinvested dividends increase my ACB?
Yes. When dividends or distributions are automatically reinvested to buy more units (a DRIP), you are effectively buying more shares with money you have already been taxed on. Those purchases add to your ACB. Forgetting reinvested distributions is the most common ACB mistake — it makes your cost base look too low and causes you to overpay capital gains tax when you eventually sell.
What is return of capital and how does it affect ACB?
Return of capital (ROC) is a distribution that is not income — it is a portion of your own capital being returned. ROC is not taxed when you receive it; instead it lowers your ACB. A lower ACB means a larger capital gain (or smaller loss) when you sell. Many ETFs and REITs distribute ROC, shown in box 42 of a T3 slip, so it is easy to miss and quietly increases your eventual gain.
Do I have to pool ACB across accounts?
Yes, for identical securities in non-registered accounts. The CRA requires you to combine all units of the same security across all your taxable accounts into a single average cost base. You cannot keep a separate ACB per brokerage. Registered accounts (TFSA, RRSP) are excluded because gains there are not taxed. This pooling rule trips up investors who hold the same ETF at two brokerages.
What tools can track ACB for me?
For Canadian investors, ACB tracking websites and spreadsheets are the most common tools, and crypto investors usually need dedicated crypto tax software. Brokerage T5008 slips often show proceeds but not an accurate cost base, especially across accounts, so you cannot rely on them alone. Keeping your own running record — every buy, reinvested distribution, and return of capital — is the only way to be sure.
This guide is for educational purposes only and is not financial or tax advice. It describes the general rules for tracking adjusted cost base under 2026 figures, including the average cost method and the pooling rule for identical properties. Special rules apply to superficial losses, identical properties acquired before 1972, and certain corporate actions. Confirm the current rules with the CRA or a qualified tax professional before acting. See our capital gains tax explained guide for the broader picture.