T5008 box 20 is not your adjusted cost base

Every year your brokerage sends you a T5008, and box 20 on it carries a number labelled cost or book value. It looks like the number you need. Very often it is not.

You do not have to take that from us. CRA tells the brokers who prepare the slip, in its instructions for completing box 20:

"This amount may or may not reflect the investor's ACB for the purpose of determining their gain or loss from the disposition of the security."

That is CRA, in the guidance it gives the people filling in the slip. It is worth knowing before you copy the number onto your return.

What box 20 actually contains

CRA defines it as "the total amount paid to purchase a security, including any transaction charges related to the purchase, adjusted for reinvested distributions, returns of capital and corporate reorganizations."

So it is not a naive purchase price. A brokerage that does this well is already adjusting for the two things people most often forget. Box 20 is a serious attempt at your cost base. It is simply an attempt made from one institution's records.

The four places it comes apart

It sees one account. This is the big one, and it is arithmetic rather than carelessness. Canada pools identical property per taxpayer, not per account. If you hold the same ETF at two brokerages, neither one's box 20 can be correct, because neither can see the other's units. Adjusted cost base, explained works through why the pool has that shape.

Transferred-in positions arrive with whatever came with them. When you move a holding between institutions, its cost base travels as a number supplied by the previous one, or gets estimated, or reset to the transfer-date price, or lost. The receiving brokerage reports what it was given.

Return of capital may not have been applied. ROC reduces your cost base rather than being taxed as income, and it arrives on a T3 slip in the spring, often after the statements it should have adjusted.

Corporate actions get recorded inconsistently. Splits, mergers and especially spin-offs require cost base to be allocated between securities under specific rules, and a spin-off allocation is a judgement call based on the issuer's own guidance.

What CRA expects of the two parties

CRA asks the slip preparer to "take reasonable measures in order to ensure that the amount reported in box 20 is correct", and separately tells the investor they "may have to make adjustments to the amount indicated in box 20 at the time of determining and reporting their gain or loss."

That is the whole relationship in two sentences. The brokerage does its best from what it holds. The figure you report is yours, and so is the liability if it is wrong.

What to do about it

Keep the trade-level record, every buy, sell, distribution and corporate action, for as long as you hold the security plus six years after you dispose of it. Monthly statements are not that record, and the ACB tracker is one way to keep it across every account rather than per statement.

Check your T3 slips each year for return of capital and reinvested distributions, and apply the adjustment in the year it happens rather than reconstructing it a decade later.

If the same security sits at more than one institution, maintain the pool yourself, because no single brokerage is positioned to. To run one security's pool through the arithmetic, the adjusted cost base calculator does it in your browser, and how Luum tracks adjusted cost base sets out which adjustments Luum applies automatically and which it leaves to you.

Once you have your own figure, the T5008 and cost base checker puts it beside box 20 on each slip and shows what the difference does to the totals you would report.

And if the disposition in question was a loss, the superficial loss rule may change the answer again.

When box 20 is blank, zero, or obviously wrong

A missing box 20 is common and it is not an error on the slip. The broker is required to take reasonable measures to report a correct figure; where it holds no reliable cost, leaving the box empty is more honest than inventing one.

The three situations that produce it:

• The position was transferred in and no cost came with it. The receiving institution has the shares and not their history.
• The security was acquired outside the account — from an employer plan, an inheritance, a gift, or a certificate deposited long after purchase.
• The broker cannot resolve a corporate action, most often an older spin-off where the allocation was never applied to its records.

A blank box changes nothing about what you owe. The reporting obligation is yours in every case, and it is identical whether the box is empty, populated, or populated wrongly. What a blank box removes is the false comfort of a number that looked authoritative.

If the box is zero rather than empty, treat that as a claim that the shares cost nothing, which is almost never true and would maximise your reported gain.

Reconciling a slip against your own record

Work in this order, because each step explains a difference the next one cannot.

1. Match the disposition first, not the cost. Confirm the security, the settlement date and the quantity on the slip against your record. A slip that describes a different disposition than you think it does makes every cost comparison meaningless.
2. Pool across institutions before comparing anything. If the security is held at more than one broker, no single box 20 is comparable to your figure by construction. Compare your pooled cost base to the sum of what you hold, not to one slip.
3. Apply return of capital for the year, from the T3, not from the monthly statements. This is the single most common source of a gap, and it moves in one direction only: ROC lowers your cost base and raises your gain.
4. Then look at what remains. A residual difference usually traces to a transfer, a corporate action, or reinvested distributions the broker did not see.

A difference is not evidence that either party made a mistake. Box 20 is an account-local number and your adjusted cost base is a taxpayer-level one, so the two are only expected to agree in the simplest case: one security, one account, held from purchase to sale with no distributions and no corporate actions.

The T5008 and cost base checker runs that comparison slip by slip and shows what each difference does to the totals you would report.

This is educational information about how the slip works, not tax advice. Verify with the CRA or a qualified tax professional before you file.

Box 20 diverges most reliably when you hold the same security at more than one institution, since no broker can see the other side, pooling cost base across two brokerages works that case through.

The label on the box, cost or book value, is its own source of confusion, and book value is not your adjusted cost base separates the two terms properly.

Common questions

What if box 20 on my T5008 is blank?

A blank box 20 means your broker holds no cost figure it considers reliable, which most often follows a transfer in from another institution, an acquisition outside the account such as an inheritance or an employer plan, or an unresolved corporate action. It is not an error and it does not change your obligation. You report your own adjusted cost base either way, so the practical effect is that you must reconstruct the figure from your own records rather than starting from the broker's.

Why is box 20 zero on my slip?

Zero is a claim that the security cost nothing to acquire, which is almost never accurate and would report the entire proceeds as a gain. Treat it the same way as a blank box: compute your own adjusted cost base from your purchase records, reinvested distributions and any return of capital, and report that. If you cannot reconstruct the cost, the broker may be able to supply the underlying transaction history even where it cannot certify a cost figure.

How many T5008 slips should I get?

One slip is issued for each disposition, so an account that sold the same security four times over the year generally produces four slips, and holding securities at several institutions produces slips from each. They are information returns the CRA also receives. Reconciling them against your own record matters most where the same security appears on slips from more than one institution, because that is exactly the case no single broker can report correctly.

Is box 20 on my T5008 my adjusted cost base?

No, and the CRA says so directly. Box 20 carries the cost or book value your broker holds, which is an account-local number. Your adjusted cost base is a taxpayer-level figure. Box 20 is a useful starting point for reconciliation and it is not the number you are obliged to report.

Why would box 20 differ from my own records?

The common causes are a transfer in from another institution where the original cost did not travel with the shares, a return-of-capital distribution that lowered your cost base without the broker adjusting for it, and holding the same security at more than one institution so that no single broker sees the whole pool.

Which figure do I report on Schedule 3?

Your own adjusted cost base, computed across all of your accounts. If it differs from box 20, keep the working that reconciles the two so you can support the number you filed. The slip is information the CRA also receives, not a determination of your cost base.