If a reportable securities transaction is processed, you may receive a T5008 slip. Box 20 gives the preparer’s cost or book value, while Box 21 gives proceeds of disposition or settlement amount.
Box 20 is not automatically wrong, and it is not automatically your adjusted cost base. CRA’s wording is more precise: Box 20 may or may not reflect the investor’s ACB. The practical task is to compare it with a complete, independently supported ledger and explain any difference before completing Schedule 3.
Written and researched by myCostBase. Last reviewed: September 2, 2026. This article was checked against current CRA, Income Tax Act and primary brokerage sources listed below. The reconciliation framework is usable without the product.
What Box 20 and Box 21 report
| T5008 field | What it reports | How to use it |
|---|---|---|
| Box 20 | Cost or book value | Compare it with the ACB supported by your complete records. |
| Box 21 | Proceeds of disposition or settlement amount | Verify it against the sale confirmation, including currency and commission treatment. |
For the field definitions without the full reconciliation, see T5008 Box 20 vs Box 21.
CRA tells T5008 preparers to take reasonable measures to include purchase transaction charges and to adjust cost for reinvested distributions, return of capital and reorganizations. That makes Box 20 a meaningful cross-check.
CRA also tells individual investors that Box 20 may or may not reflect ACB and that they must make any adjustments needed for tax reporting. A broker cannot include information it does not have, such as identical holdings at another institution or historical facts that were never transmitted.
Why Box 20 can differ from ACB
The direction of the difference matters. A cause should not be labelled “higher” or “lower” unless its effect is actually known.
| Possible cause | Usual effect on broker Box 20 compared with supported ACB | Why |
|---|---|---|
| ROC reduction missing or not yet posted | Higher | Positive ROC or another positive Box 42 adjustment reduces ACB. Omitting the reduction leaves book cost too high. |
| Reinvested or non-cash distribution missing | Lower | The taxable reinvested amount generally increases ACB. |
| Purchase commission missing from cost | Lower | Purchase transaction charges generally form part of cost. |
| Identical-property purchase at another brokerage | Depends | A purchase above the existing average raises ACB per unit; a purchase below it lowers the average. |
| Transfer history missing, estimated or corrected | Depends | The displayed value depends on what data was transmitted or supplied. |
| DRIP or transaction outside the broker’s records | Depends | The purchase changes both the pooled cost and unit balance; the per-unit effect depends on price. |
| Corporate action or reorganization | Depends | The tax result depends on the event and available elections or allocations. |
| Foreign-currency conversion difference | Depends | Transaction dates, rate sources and currency presentation can change the CAD result. |
Do not force the ledger to match Box 20. Identify the specific missing or differently treated event and keep its supporting source.
For broker-displayed values and current brokerage documentation, see Broker Book Value vs Adjusted Cost Base. For ETF adjustments, see ETF Return of Capital and Adjusted Cost Base.
When Box 20 is useful
Box 20 can:
- confirm that the broker has a non-zero basis on file;
- reveal missing or estimated transferred cost;
- identify a difference worth investigating;
- corroborate an independent ledger in a simple, complete history;
- show whether an annual adjustment may not yet have been posted.
It is more likely to agree with supported ACB when the security was acquired and held entirely at one institution, all transfers and corporate actions are documented, annual adjustments are posted, and the taxpayer has no identical holdings at another taxable brokerage.
Agreement is useful evidence. It is not proof that facts outside the broker’s records were included.
Reconciliation workflow
For each disposition:
- Match the T5008 security and settlement date to the sale confirmation.
- Verify the quantity and Box 21 proceeds, including the currency reported.
- Determine whether a selling commission is already netted from Box 21.
- Build the complete chronological history across all taxable accounts under the same ownership.
- Apply purchases, purchase commissions, sales, DRIPs, transfers, corporate actions, ROC and reinvested-distribution adjustments.
- Calculate the pooled ACB immediately before the sale without prematurely rounding ACB per unit.
- Multiply that exact per-unit ACB by the units sold.
- Compare the supported ACB for the units sold with Box 20.
- Record the amount, direction and documented cause of the difference.
- Transfer the supported proceeds, ACB and outlays or expenses to Schedule 3.
The T5008 ACB reconciliation checker can compare Box 20 with your independently calculated ACB. The Canadian Adjusted Cost Base Checklist provides the complete source-document and accountant-handoff workflow.
Worked example: T5008 to ACB to Schedule 3
Assume all acquisitions below occurred before the 2022 ROC record date and all 256 units were entitled to that distribution:
| Event | Units | Cost-base effect | Running units | Running ACB |
|---|---|---|---|---|
| 2019 purchase: 200 units at $22.00 | +200 | +$4,400.00 | 200 | $4,400.00 |
| 2021 purchase: 50 units at $26.00 | +50 | +$1,300.00 | 250 | $5,700.00 |
| 2021 DRIP: 6 units at $24.00 | +6 | +$144.00 | 256 | $5,844.00 |
| 2022 ROC: $0.30 × 256 entitled units | 0 | −$76.80 | 256 | $5,767.20 |
Exact ACB per unit before sale:
$5,767.20 ÷ 256 = $22.528125
The investor then sells 100 units at $33.00 with a $9.95 selling commission.
Assume, for illustration, that the broker included all three acquisitions but had not posted the ROC reduction. Its cost for 100 units would be:
$5,844.00 ÷ 256 × 100 = $2,282.81
That amount is the example’s documented Box 20. It is not an unexplained figure.
Reconciliation
| Item | Amount |
|---|---|
| T5008 Box 21 gross proceeds | $3,300.00 |
| T5008 Box 20 cost/book value | $2,282.81 |
| Supported ACB for 100 units | $2,252.81 |
| Box 20 minus supported ACB | $30.00 |
| Selling commission | $9.95 |
The $30 difference is exactly the missed ROC attributable to the 100 units sold:
$76.80 ÷ 256 × 100 = $30.00
What goes on Schedule 3
| Schedule 3 column | Amount |
|---|---|
| Proceeds of disposition | $3,300.00 |
| Adjusted cost base | $2,252.81 |
| Outlays and expenses | $9.95 |
| Capital gain | $1,037.24 |
The example preserves full precision until the displayed amounts:
$3,300.00 − $2,252.8125 − $9.95 = $1,037.2375, displayed as $1,037.24.
This example assumes Box 21 contains gross proceeds. CRA instructs T5008 preparers not to deduct disposition expenses from Box 21, but broker documentation can differ. If the actual slip already nets the commission, do not deduct it a second time.
What records support the reconciliation?
Keep the records that explain both the calculation and the discrepancy:
- original purchase and sale confirmations;
- statements showing transaction and unit history;
- transfer documents and the outgoing statement;
- DRIP confirmations;
- T3 details and issuer tax-character documents;
- corporate-action notices;
- foreign-currency rate source and transaction-level calculation;
- the chronological ACB ledger;
- the T5008-to-Schedule-3 reconciliation.
CRA’s general rule is to keep supporting records for six years from the end of the last tax year they relate to. CRA separately says records concerning long-term acquisitions and dispositions, and other historical information that can affect a later sale, should be kept indefinitely.
What if Box 20 is blank or zero?
A blank or zero Box 20 does not mean ACB is zero. It means no usable cost was reported in that field.
Reconstruct the cost from the available purchase confirmations, statements, transfer records and adjustment documents. If the amount is material and cannot be supported, seek professional advice rather than substituting current market value or zero.
Sources and calculation notes
- CRA: T5008 Guide—Return of Securities Transactions
- CRA: T5008 slip information for individuals
- CRA: Completing Schedule 3
- CRA: Capital Gains—T4037
- CRA: Tax treatment of mutual funds
- Income Tax Act, section 47—Identical Properties
- CRA: How long to keep records
- Interactive Brokers Canada: Tax information and reporting
The amounts above were independently recalculated and retain full precision until display. Corrections or source updates can be reported through the myCostBase contact page.
The application can compare recorded ACB with T5008 values, but the result still depends on complete transactions and supporting adjustments. Use the free T5008 reconciliation checker →
Frequently asked questions
Is T5008 Box 20 the same as my adjusted cost base?
Not necessarily. CRA says Box 20 may or may not reflect the investor’s adjusted cost base. It can be a useful cross-check, but the taxpayer must make any adjustments needed for complete holdings, transfers, distributions and other events.
What should I report on Schedule 3?
Report the supported proceeds, adjusted cost base and outlays or expenses for the disposition. Verify Box 21 against the sale confirmation, calculate ACB from the complete record, and make sure a selling commission is not deducted twice.
When is T5008 Box 20 useful?
Box 20 is most useful as a cross-check when the position has a complete single-broker history, transferred cost is supported, annual adjustments have been posted and there are no identical holdings at another taxable brokerage. Agreement is corroboration, not proof that all external information was included.
What if my ACB is higher than T5008 Box 20?
A higher supported ACB generally produces a lower capital gain or larger capital loss. Possible causes include a missing purchase commission, reinvested distribution or transaction outside the broker’s records. The direction depends on the complete history, so document the actual cause rather than assuming one.
General information only — not tax, legal, or financial advice. Consult a qualified professional for advice specific to your situation.