Tax · Canada
Superficial loss calculator.
You sold shares at a loss and bought the same shares back close to the sale. Find how much of the loss CRA denies and what gets added to your cost base.
Denied loss = least of S, P and B ÷ S × L. S is shares sold, P is shares bought in the 61-day window (30 days before, the sale day, 30 days after), B is shares still held at the end of it, and L is your loss. The denied amount is added to the adjusted cost base of the shares you still hold.
Inputs
Result
Enter your details and press Calculate.
How the superficial loss rule works
A loss on capital property is superficial when you, or a person affiliated with you, buy the same or identical property in the period starting 30 calendar days before the sale and ending 30 calendar days after it, and you or that person still own it 30 calendar days after the sale. A superficial loss cannot be deducted. Whoever acquires the substituted property can usually add the denied amount to its adjusted cost base, so the loss is deferred, not lost.
When fewer shares are repurchased and held than were sold, CRA administratively accepts a partial denial: SL = (least of S, P and B) ÷ S × L. S is the number of shares sold, P the number acquired in the 61-day period, B the number left at the end of the period, and L the loss otherwise determined. Example: sell 80 shares for a $80 loss, buy 50 in the window and hold 90 at the end. The least of 80, 50 and 90 is 50, so 50 ÷ 80 × $80 = $50 is denied and $30 is allowed.
Not modelled: the exceptions CRA lists (becoming or ceasing to be a Canadian resident, death, option expiry and others), whether two securities are identical, and repurchases inside an RRSP or TFSA. Confirm those with CRA.
Sources, fetched 29 September 2026: CRA — Guide T4037, Capital Gains (Superficial loss); CRA External T.I. 2005-0150811E5 (the S, P, B formula), as published by Tax Interpretations.
Frequently asked questions
Is the 30-day rule really 61 days?
Yes. The window runs 30 calendar days before the sale to 30 calendar days after it, and CRA counts the acquisitions in that 61-day period.
Do I lose the denied amount?
Not usually. CRA says you can generally add the superficial loss to the adjusted cost base of the substituted property, which lowers your gain or raises your loss when you finally sell it.
Does my spouse's purchase count?
Yes. CRA lists your spouse or common-law partner, and a corporation you or they control, as affiliated persons whose purchases count.
Estimate only — not tax advice
This tool applies CRA's published formula to the figures you enter. It does not check affiliation, identical-property status or the exceptions, so confirm your situation with CRA or a tax professional.