A worked example
A $400,000 mortgage at 5.5% over a 25-year amortization comes to about $2,441.57 a month under Canada's semi-annual compounding rule — versus roughly $2,456.35 if a US-style monthly-compounding calculator were used instead on the same nominal rate.
Frequently asked questions
Why does Canada use semi-annual compounding at all?
It's a long-standing requirement under the federal Interest Act, which mandates that mortgage interest be expressed as compounded no more than semi-annually unless stated otherwise — a consumer protection rule with roots going back over a century.
Does semi-annual compounding cost more or less than monthly compounding?
Slightly less, for the same nominal annual rate — converting a semi-annual rate to its equivalent monthly rate produces a number a touch below simply dividing the annual rate by 12, which is what a US-style calculator would do.
Is the difference large enough to matter?
It's a small effect per month, but it compounds (quite literally) over a 25-30 year amortization — using a US mortgage calculator for a Canadian mortgage will slightly overstate the true payment and total interest.
This calculator provides estimates for general informational purposes only and is not financial advice.