Canada's superficial-loss rule denies a loss if you (or an affiliate) rebuy identical property within 30 days.
What it is
The superficial loss rule (Income Tax Act s.54) prevents an investor from claiming a capital loss when the position is effectively maintained rather than truly exited. A loss is "superficial" if, during the period 30 days before to 30 days after the sale, you or an affiliated person acquire the identical (or an identical) property and still own it at the end of that window. It is Canada's counterpart to the US wash-sale rule.
Why it matters
It directly limits tax-loss harvesting: a loss you thought you "banked" can be silently disallowed, leaving you with a tax bill you did not plan for. The biggest pitfall is the broad "affiliated person" net — your spouse or common-law partner, a corporation you (or your spouse) control, and your own RRSP/TFSA/RRIF/FHSA all count, so a rebuy in any of those tied accounts triggers the rule even though you personally did not repurchase. Worse, when the repurchase lands inside an RRSP or TFSA, the loss is denied permanently rather than just deferred.
How it's calculated
There is no formula — it is a conditional test, not a calculation. Check whether you or an affiliated person bought the identical property in the 61-day window (30 days before through 30 days after the disposition) and still held it at the window's end; if both are true, the loss is denied. The disallowed loss is normally added to the adjusted cost base (ACB) of the substituted property, deferring it until that property is finally sold (the exception: if the rebuy is in an RRSP/TFSA, the loss is lost outright).
How Quintarthai uses it
When reviewing a holding's tax lots or planning a year-end sale, open the company's deep-analysis page at /app/ to confirm the security and any cross-listed equivalents, and read the linked wash-sale-rule entry in the Knowledge Base to compare the Canadian and US timing windows side by side.
Cross-border note. Both countries use a 30-day-before-and-after window, but Canada's "affiliated person" scope is broader than the US wash-sale rule (IRC s.1091): it explicitly reaches your spouse/common-law partner, a corporation you control, and your registered accounts. In Canada a deferred loss is added to the substituted property's ACB; the US similarly adds the disallowed loss to the basis of the replacement shares, but Canadian capital losses generally offset only capital gains (not ordinary income), whereas a US investor may deduct up to US$3,000 of net capital losses against ordinary income annually.
FAQ
I sold a stock at a loss and rebought it 35 days later. Is my loss safe?
Yes. The rule only catches a repurchase within 30 days before or after the sale that you still hold at the window's end. Waiting more than 30 days past the sale (and ensuring no affiliated person bought inside the window) preserves the loss.
Can I sell at a loss in my non-registered account and immediately rebuy the same stock in my TFSA?
No — that triggers a superficial loss because your TFSA is an affiliated person. Worse, because the rebuy is inside a registered account, the loss is denied permanently rather than just deferred into ACB.
Check your understanding
On December 10 you sell 100 shares of a Canadian bank at a $4,000 loss in your taxable account. On December 20 your spouse buys 100 of the identical shares and still holds them on January 15. What happens to your loss?
Your spouse is an affiliated person, the rebuy fell inside the 30-day window, and the shares were still held at the window's end, so the loss is superficial and added to the substituted property's ACB.