The T5008 problem, stated plainly
Every time you sell, your broker files a T5008 slip, and CRA's matching program compares those slips to your return. Proceeds usually reconcile. Cost usually does not: box 20 is often empty, shows book value inherited from a transfer instead of true cost, or averages lots differently than the Income Tax Act requires. A trader with three thousand fills across Interactive Brokers and Questrade can be out by tens of thousands of dollars without one dishonest entry.
The platform P&L compounds it. Platforms report performance per position, per account, usually in trade currency. Canadian tax wants each disposition in Canadian dollars at the exchange rate on the day of the transaction, using one pooled cost base per identical security. Those are different ledgers, and only one of them is the law. A trade that closed flat in US dollars can still be a real Canadian-dollar gain or loss once the Bank of Canada rates are applied to each leg.
| Record | What it gives you | What it misses |
|---|---|---|
| T5008 slips | The proceeds CRA will match against | Reliable cost; box 20 is often blank or book value |
| Platform P&L | Performance by position | CAD conversion, pooled ACB, other accounts |
| Monthly statements | Margin interest and fees by account | Any tie-in to what the return reports |
| A maintained ACB ledger | One CAD cost base per security, every account | Nothing; the return is built from it |
One adjusted cost base per security, across every account
Identical properties carry a single weighted-average adjusted cost base across all of your non-registered accounts. Hold the same ticker at two brokers and the ACB blends; the per-account book value each broker displays stops being the tax answer. Transfers between institutions arrive carrying whatever figure the sending side passed along, frequently market value on the transfer date rather than anything you paid.
The ledger also has to absorb everything a real trading year throws at it:
- Splits, consolidations and spin-offs that restate share counts and cost
- Dividend reinvestment purchases, each one a new lot at a new price
- Option premiums, which adjust cost or proceeds on assignment instead of standing alone
- US-dollar settlement, converted trade by trade, not at one year-end rate
Superficial losses are a records problem before they are a tax problem
A capital loss is denied when you, your spouse or an account affiliated with you, including your own RRSP or TFSA, buys the identical security in the window running 30 days before the sale to 30 days after, and still holds it at the end. Active traders trip this constantly, because re-entering a setup two weeks later is normal trading behaviour. The denied loss is added to the cost base of the replacement shares, so it usually comes back later. Buy the replacement inside a TFSA or RRSP and it never comes back at all.
Catching this means seeing every account in one place: yours, your spouse's and the registered ones. We flag open windows in December, while there is still time to let one close, instead of discovering them in April when nothing can be done.
Margin interest, and the paper trail behind it
Interest on money borrowed to earn income is deductible: as a carrying charge on line 22100 when your gains are capital, on the T2125 when the trading is business income. Deductibility follows what the borrowed money actually bought, so a margin balance that also funded personal spending contaminates the trace. We keep trading leverage in accounts that fund nothing else, and post interest by account every month.
Commissions surprise people on capital account: they fold into cost and proceeds rather than being deducted as an expense, and data feeds or charting software are generally not deductible at all unless the trading is a business. Which answer applies is the character question, the subject of our trader tax filing page; the accounting job is making sure that whichever way it lands, the numbers underneath are already clean.
What year-round looks like
End-to-End Accounting for a trader is not invoicing and payroll; it is a monthly tie-out. Statements land, trades import, exchange rates apply, interest posts where it belongs and the ACB ledger rolls forward, so the Personal Tax Filing in April is an export rather than an archaeology dig. Most traders work alone, which is why CPA Quick Support at $99 a month fits the in-between questions: a matching letter, a broker transfer, a spouse opening an account. We work with traders across Mississauga and the GTA who wanted exactly one thing from an accountant: numbers that tie.
