How it works
Canadian mortgages calculate interest differently from loans in most other countries. By law under the Interest Act of Canada, fixed-rate mortgages compound interest semi-annually rather than monthly. This means interest accrues twice per year, not twelve times, which directly affects the effective rate you pay each month.
This matters because a 5.89% posted rate compounded semi-annually produces a lower monthly cost than the same 5.89% compounded monthly. The calculator converts your annual rate into a semi-annual rate first, then derives the equivalent monthly rate from that. It then applies standard amortization math to determine your fixed monthly payment over the full amortization period.
Note that this calculation produces the principal and interest payment only. It does not include property taxes, home insurance, CMHC mortgage default insurance premiums, or condo fees, which most lenders collect alongside your payment.
The formula
Monthly Payment = P × [ r_m × (1 + r_m)^n ] / [ (1 + r_m)^n − 1 ]
Where:
- P = mortgage principal amount
- r_m = equivalent monthly rate, derived from the semi-annual rate
- n = total number of monthly payments (amortization years × 12)
To get the equivalent monthly rate from the Canadian semi-annual convention:
- Divide the annual rate by 2 to get the semi-annual rate:
r_s = annual_rate / 2 - Convert the semi-annual rate to a monthly equivalent:
r_m = (1 + r_s)^(1/6) − 1
The exponent of 1/6 appears because there are six monthly periods in each semi-annual compounding interval.
Worked example
A buyer purchases a C$450,000 home with a 5-year fixed term inside a 25-year amortization at 5.89% interest, compounded semi-annually.
Step 1: Determine the semi-annual rate.
r_s = 0.0589 / 2 = 0.02945 (2.945% per half-year)
Step 2: Convert to the equivalent monthly rate.
r_m = (1 + 0.02945)^(1/6) − 1
r_m = (1.02945)^0.16667 − 1
r_m = 1.004845 − 1 = 0.004845 (0.4845% per month)
Step 3: Determine the total number of payments.
n = 25 years × 12 = 300 monthly payments
Step 4: Calculate the monthly payment.
Payment = 450,000 × [ 0.004845 × (1.004845)^300 ] / [ (1.004845)^300 − 1 ]
Payment = 450,000 × [ 0.004845 × 4.2589 ] / [ 4.2589 − 1 ]
Payment = 450,000 × 0.020635 / 3.2589
Payment = 450,000 × 0.006331
Payment = C$2,849.03 per month
Over the 5-year term (60 payments), you pay roughly C$170,942 total. Of that, about C$43,700 goes to principal and C$127,242 goes to interest, leaving a balance of approximately C$406,300 at renewal.
Things to watch
The most common mistake is treating the Canadian annual rate as if it compounds monthly. If you simply divided 5.89% by 12, you would get 0.4908% per month. The correct semi-annual-derived rate is 0.4845%—a difference that shifts the payment on a C$450,000 loan by roughly C$18 per month, or over C$5,000 across the full 25-year amortization.
Also note that the 5-year term and 25-year amortization are distinct concepts. Your payment is calculated to fully retire the loan over 25 years, but the interest rate is only guaranteed for 5. At renewal, you refinance the remaining balance at whatever rate prevails then, producing a new payment for the next term.
Finally, the semi-annual compounding convention applies to fixed-rate Canadian mortgages by law. Variable-rate mortgages may compound monthly or daily depending on the lender, so verify which convention your specific product uses before relying on this calculation.
This calculator provides a payment estimate for planning purposes and does not constitute professional financial advice. Actual lender calculations, rounding, and fee structures may produce slightly different figures.