BMO InvestorLine adjusted cost base

An account with two names on it is still two taxpayers, and that is the whole difficulty. The account has one balance, one statement and one slip. The tax return that reports it does not.

None of this is a problem with any broker. It is what the rule asks for, and it is the part a statement is structurally unable to answer for you. For the calculation itself, read adjusted cost base explained first.

One account, two names, one slip

For investment income credited to a joint account, a single slip is issued. It carries one holder's identification number, and a code telling the CRA the account is joint.

So the slip records that the account has more than one owner and does not record how the income divides between them. That is not an oversight. CRA is explicit about where the responsibility sits, in the instructions it gives the institutions that prepare the slip:

"Where there are multiple (two or more) account holders for the same account, the onus is on the account holders to ensure that each individual reports their fair share of the income."

That is CRA telling the preparer that the split is not its job. It is yours, and so is the support for it.

The share you report is based on how much you contributed, not on whose name appears first and not on an even division by default.

This is where the intuition goes wrong. Two names on an account reads like a half share each, and an equal split is simply the most common case rather than the rule. An account funded entirely by one spouse is generally that spouse's income to report, even though both names are on it, and even though the slip gives no indication of that.

The practical consequence is that contribution is a record to keep, in the same way trade confirmations are. It is the thing you would be asked for, and it is easiest to reconstruct at the time rather than years afterwards.

Adding a spouse moves neither the tax nor the cost base

This is the one worth reading carefully, because both halves of it surprise people, and they surprise them in opposite directions.

The cost base does not reset. A transfer of property to a spouse happens automatically at your adjusted cost base rather than at market value. Nothing is realised, which is usually welcome, and it also means no step up: your spouse's cost base for that holding is your cost base, carrying every purchase, every reinvested distribution and every return of capital that built it.

The tax does not move either. Where property has been transferred to a spouse, the income and the capital gains on it are generally attributed back to the person who transferred it. So the gain on an eventual sale is reported by the transferor, not by the spouse whose name was added, and the attribution follows the property rather than ending at the transfer.

Two consequences follow, and they are the opposite of the obvious reading:

Adding a spouse to an account is not a way to split a gain. Attribution is the rule the arrangement runs into, and it applies whether or not anyone intended a tax result.
It is possible to elect out and treat the transfer as a disposition at market value instead, which realises the gain immediately and stops the attribution. That is a deliberate choice with a tax cost now, and it is a conversation to have with an accountant rather than a box to tick.

⚠️ A joint owner who is not your spouse is a different calculation. Adding an adult child or a parent does not use the spousal rollover, and the attribution rules treat the relationships differently. This page does not rule on that case.

Identical property pools per taxpayer, not per account, and a joint account does not sit outside that.

Your share of a security held jointly pools with your holdings of the same security anywhere else, including in an account with only your name on it. Neither account displays that combined figure, because neither one has the information to.

Adjusted cost base across two brokerages works through the arithmetic of pooling in both directions. A joint account adds one step before it: establish your share first, then pool that share with the rest of what you own.

Reading the slip against your own number

A T5008 reports proceeds per account, and box 20 is where a cost amount would sit. On a joint account the mismatch is structural rather than accidental, since the slip describes the account and your return describes you.

T5008 box 20 and your ACB explains how to read the two together, and the T5008 and cost base checker shows the Schedule 3 totals each version implies.

Getting the history into one place

BMO InvestorLine is a supported read only connection in Luum, so the account can be linked rather than typed, and its transaction history is what a cost base is built from. The connection can see positions and transactions and cannot place a trade or move cash.

If you prefer not to connect it, every plan takes a holdings upload and a transaction history import. For cost base the distinction matters: a holdings snapshot shows what the account owns now, and an average cost needs every purchase that built it. The ACB tracker keeps that pooled record across every account you hold.

What no tool decides for you is the share. Luum tracks the holdings and the transactions in an account; the proportion of a jointly held account that belongs on your return follows from who contributed, which is a fact about you rather than about the account.

This page is educational and is not tax advice. Joint ownership, attribution and spousal transfers depend on facts this page cannot know, including who funded what and when. Confirm the treatment with the CRA or a qualified tax professional before you file.

Common questions

Who reports the capital gain on a joint investment account?

Each owner reports their own share, and that share is based on how much each contributed rather than on whose name appears first or on an even division by default. The slip issued for the account does not settle it: a single slip covers the account, carries one holder's identification number and a code identifying it as joint, and the CRA is explicit that the onus is on the account holders to ensure each individual reports their fair share. An equal split is the most common outcome, not the rule.

Does adding my spouse to my account split the tax?

Generally no. A transfer of property to a spouse happens at your adjusted cost base rather than at market value, so nothing is realised at the time, and the income and capital gains on that property are generally attributed back to you as the person who transferred it. The gain on a later sale is therefore reported by you rather than by the spouse whose name was added. Electing out of that treatment is possible, and it means realising the gain immediately, which is a decision to take with an accountant.

Does my spouse get a new cost base when I add them to an account?

No, and this is the half people find surprising. The property moves at your adjusted cost base, not at what it is worth on the day, so there is no step up. Your spouse inherits the cost base you built, including every reinvested distribution and every return of capital that reduced it along the way. That matters most on a holding that has appreciated significantly, because the deferred gain travels with it.

How do I prove how much each person contributed?

Keep the record at the time rather than reconstructing it later. Deposits, transfers into the account and the source of the funds are what establish the share, and they are far easier to evidence in the year they happen than a decade afterwards. This is the same discipline that applies to trade confirmations, and for the same reason: the number you file is one you may be asked to support.

Do I need to track cost base in a joint TFSA or RRSP?

Neither account can be held jointly, which settles the question. Adjusted cost base matters in a non-registered account, because that is where a capital gain is realised and reported, and registered accounts do not produce capital gains to report. A jointly held non-registered account is where all of the above applies.