Tax result
Covered call expired worthless
Capital gain / loss
$250.00
On capital account, the $250.00 premium is proceeds when the option is written. After $0.00 of opening fees, the grant-date gain is $250.00. Expiry creates no replacement share transaction, so your stock ACB is unchanged.
CRA treatment: Capital-versus-income treatment depends on the taxpayer's facts. On capital account, a holder's expiry produces a loss, while a writer's premium is proceeds at grant; assignment adjusts underlying proceeds or ACB and may require a prior-year amendment.