Accurate capital gains reporting depends on adjusted cost base (ACB). But ACB tracking can break down when clients have reinvested distributions or return of capital. Broker statements often miss those adjustments, so you end up rebuilding ACB from slips, fund notices, and trade confirmations.
This guide gives you a simple ACB formula, a corrected running ledger example, and an adjustments checklist. You will also see how ACB changes after-tax proceeds, which helps you support better retirement and withdrawal decisions.
Main takeaways
- ACB is the tax cost of a security in a non-registered account. Broker “book cost” can miss key adjustments, so it is not always reliable.
- Track total ACB and ACB per unit in a running ledger. Update both after every purchase, DRIP, reinvested distribution, or adjustment.
- Use average cost for identical properties in the same account. Recalculate ACB per unit after each acquisition before you model a sale.
- Return of capital lowers ACB and can create a deemed capital gain if ACB drops below zero. T3 box 42 and fund tax breakdowns help you capture those changes.
- ACB drives the capital gain and the after-tax proceeds your client keeps. That after-tax result can change withdrawal timing, benefit thresholds, and retirement planning decisions.
What ACB means for Canadian tax reporting
ACB is the total tax cost of a security in a non-registered account. It usually starts with purchase cost plus commissions. It then changes over time due to items like reinvested distributions and return of capital.
Broker “book cost” can be a starting point, but it is not always reliable. CRA says the amount in T5008 box 20 may or may not reflect ACB, and you are responsible for the adjustments when you report gains and losses.
Terminology note: In this guide, ACB means Canadian adjusted cost base under CRA rules.
How to calculate ACB: key formulas
You will track two numbers: total ACB and ACB per unit. Update both after every purchase, DRIP, reinvested distribution, or ACB adjustment.
Total ACB formula
Total ACB =
Purchase costs + commissions and fees + ACB increases
minus ACB decreases
Typical increases include:
- DRIP purchases
- reinvested distributions
- denied losses added back under the superficial loss rule
Typical decreases include:
- return of capital
- the ACB of units sold in a partial sale
ACB per unit formula
ACB per unit = Total ACB ÷ Total units held
For identical properties, CRA generally expects an average cost approach that updates as you buy more units. This average cost method typically applies across all non-registered accounts held by the same taxpayer, not just one brokerage account, so it is worth checking for the same ETF at multiple institutions.
Capital gain at sale
Capital gain (or loss) =
Proceeds of disposition − ACB of units sold − outlays and expenses
Outlays and expenses include selling commissions.
Move from ACB cleanup to a plan clients can act onOnce you have clarified the non-registered holdings, the next step is gathering the rest of the client inputs and building a scenario. The Snap Projections Toolkit includes editable templates to help streamline client data collection and new plan setup. |
Working example with a running ACB table
A running ledger helps you avoid drift between what the broker reports and what CRA expects you to report.
Example scenario
- Jan 15: buy 100 ETF units at $20 = $2,000, plus $10 commission
- Mar 10: buy 50 more units at $22 = $1,100, plus $10 commission
- Jun 1: sell 75 units at $25 = $1,875 proceeds, with a $10 selling commission
Running ACB ledger after each transaction
| Date | Transaction | Units (change → held after) | Total ACB after (CAD) | ACB per unit after (CAD) |
|---|---|---|---|---|
| Jan 15 | Buy | +100 → 100 | 2,010 | 20.10 |
| Mar 10 | Buy | +50 → 150 | 3,120 | 20.80 |
| Jun 1 | Sell (partial) | −75 → 75 | 1,560 | 20.80 |
Capital gain on the Jun 1 sale
- ACB of units sold = 75 × 20.80 = $1,560
- Net proceeds = 1,875 − 10 = $1,865
- Capital gain = 1,865 − 1,560 = $305
Why your ledger matters more than broker slips
As a reminder, CRA warns that T5008 box 20 may not reflect ACB. Your ledger helps you reconcile slips and defend your assumptions if CRA asks.
ACB adjustments that change the numbers
These adjustments cause most ACB errors because they often happen outside the trade confirmation.
What increases ACB
- Additional purchases, including commissions
- DRIP purchases
- Reinvested distributions
- Superficial loss add-backs
What decreases ACB
- Return of capital
- Partial sales, using ACB per unit × units sold
When ACB drops below zero
If return of capital reduces ACB below zero, CRA treats the negative amount as a deemed capital gain in that year and resets ACB to zero.
Five ACB adjustments that cause the most errors
ROC, phantom distributions, superficial losses, stock splits, and FX conversions cause the most errors. These often create gaps between your ledger and broker statements.
The table below lists five adjustments. It also provides examples of what you can log in your running ledger.
Five common adjustments and what to record
| Adjustment | Effect on total ACB | Where it shows up | What to record |
|---|---|---|---|
| Return of capital | Decrease | Fund tax breakdown, T3 box 42 | Amount, date, new ACB |
| Reinvested distribution | Increase | Fund breakdown, T3 slip | Amount, date, new ACB |
| Superficial loss | Increase | Trade confirms, cross-account review | Denied loss added to ACB |
| Stock split or consolidation | No change to total ACB | Corporate action notice | New unit count, new ACB per unit |
| Foreign currency conversion | Varies in CAD | Trade confirms, FX records | CAD values and rate source |
Return of capital and T3 Box 42
Return of capital (ROC) is not taxable when received. Instead, it reduces ACB and increases the future gain when the client sells.
On a T3, Box 42 reports ROC, and it is generally treated as an ACB reduction—so you subtract the Box 42 amount from ACB. If ROC reduces ACB below zero, the negative amount is a deemed capital gain in that year and ACB resets to zero.
Note: A negative amount in Box 42 is uncommon and may reflect a correction or another adjustment. When it occurs, it can be worth confirming against the fund’s tax breakdown.
Phantom distributions from ETFs and mutual funds
ETFs and mutual funds can allocate year-end capital gains that are reinvested. No cash hits the account, but tax can still apply, and ACB can increase.
If you miss these, ACB is often too low, which can overstate a future gain. Use the fund’s tax breakdown and the client’s T3 slip to confirm what was reinvested.
Superficial loss rule and the 30-day window
If a client sells at a loss and buys the same property within 30 days, the loss can be denied. The denied loss is added to the ACB of the replacement property. This often shows up during tax time, not at trade time.
Registered account trap to flag: If the replacement purchase happens inside a registered account, the denied loss may be effectively lost. That’s why it is often worth checking cross-account activity before you harvest losses.
Stock splits and consolidations
A split changes the unit count, not total ACB. Recalculate ACB per unit using the new unit count. Record the split ratio and effective date so your ledger stays consistent.
Foreign currency conversion for U.S. holdings
For foreign-currency trades, track ACB in Canadian dollars. Convert purchase cost, proceeds, and expenses using the rate on each trade date. Keep a note of your rate source so you can reconcile later.
From ACB to after-tax proceeds
ACB drives the capital gain you report, and that gain drives what the client actually keeps.
Capital gain reporting and inclusion rate
Taxable capital gain = capital gain × inclusion rate.
The inclusion rate is 50% under current rules. There have been proposed changes in recent years, so it is worth confirming the current inclusion rules when you are modelling multi-year scenarios.
Deemed dispositions that trigger gains and reset ACB
Certain events trigger a deemed disposition, even if no sale occurs. Common examples include death and ceasing Canadian tax residency. In these cases, capital gains are calculated using fair market value at the time of the event, and ACB resets for the next owner or period.
Donations note: Donating publicly traded securities is also a disposition. ACB still matters when you are confirming the gain on the transfer and modelling the after-tax impact.
Why ACB changes what clients keep
Two clients each sell $100,000 of the same ETF.
- Client A ACB: $80,000 → gain $20,000
- Client B ACB: $60,000 → gain $40,000
At 50% inclusion, Client B reports twice the taxable gain. That can change net cash, benefit thresholds, and withdrawal timing.
Model the tax impact of capital gainsOnce ACB is confirmed, the next step is showing clients what they will actually keep after tax. Use Snap Projections to model capital gains, OAS clawbacks, and after-tax retirement income. |
Documentation checklist for defensible ACB
A repeatable process keeps ACB clear for clients and defensible for reporting.
What to collect
- Trade confirmations for every buy and sell, including commissions
- T3 slips and fund tax breakdowns, especially box 42 adjustments
- Corporate action notices, including splits and reorganizations
- FX records for foreign-currency trades, including your rate source
What to track in your ledger
Use consistent columns:
- Date
- Transaction type
- Units bought or sold
- Cost or proceeds
- Commission
- Adjustment type (ROC, DRIP, reinvested distribution)
- Total ACB after
- Units held
- ACB per unit
- Source document reference
Update the ledger after each event—do not wait until tax season.
When to escalate
Some corporate actions are complex, including mergers, spinoffs, and reorganizations.
In-kind transfers and ownership changes can also affect ACB assumptions. If the tax treatment is not clear, it is often worth involving a qualified tax professional.
This article is educational content and does not replace tax advice for specific transactions.
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Turn accurate ACB into tax-aware retirement projections
Accurate ACB tracking helps you report capital gains correctly. It also helps you show clients what they will actually keep after tax.
Snap Projections lets you take a confirmed ACB assumption and model the tax impact of non-registered sales inside full retirement scenarios. Using Financial Planning Software for Advisors, you can compare drawdown strategies side by side and show how ACB-driven gains affect spendable income, OAS clawbacks, and estate values, without rebuilding the plan for each what-if.
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FAQs about adjusted cost base calculations
How often do I need to recalculate ACB per unit?
You must recalculate ACB per unit after every acquisition. This includes purchases, DRIPs, and reinvested distributions. CRA requires the average cost method for each transaction.
How do I calculate ACB for the units I’m selling in a partial disposition?
Multiply your current ACB per unit by units sold. Reduce your remaining total ACB by that amount.
What happens when ACB drops below zero from return of capital?
The negative amount is a deemed capital gain that year. This applies even if the client has not sold. ACB then resets to zero.
Does ACB need to be averaged across multiple non-registered accounts?
Yes. For identical properties, CRA generally expects an average cost method across all non-registered accounts held by the same taxpayer. If clients hold the same ETF at more than one institution, you will often need a single combined ledger.
Can a superficial loss be lost if the replacement purchase happens in an RRSP or TFSA?
It can be. If an identical property is repurchased in a registered account during the superficial loss window, the loss may be denied without a practical ACB adjustment. This is why cross-account review matters before tax-loss selling.
