How to Calculate Your Canadian Mortgage Payment
If you've ever plugged numbers into an online mortgage calculator and gotten a slightly different answer than your bank quoted, this article is for you. Canadian mortgages don't use the same compounding math as American mortgages, and the difference can be hundreds of dollars per year.
The one rule that changes everything: semi-annual compounding
Section 6 of the Interest Act (Canada) requires that fixed-rate mortgage interest be expressed and compounded no more than twice yearly. In practice, every Canadian fixed-rate mortgage compounds semi-annually, even though payments are made monthly. Variable-rate mortgages, by contrast, compound monthly.
That single legal sentence is why the formula your American friend uses won't give you the right number for a Canadian mortgage.
Converting an annual rate to a monthly rate
Fixed rate (semi-annual compounding):
monthly_rate = (1 + annual_rate / 2)^(1/6) − 1Variable rate (monthly compounding):
monthly_rate = annual_rate / 12The difference looks small but compounds. On a $600,000 mortgage at 5%, the fixed-rate monthly is about $3,489; the variable-rate monthly is about $3,505 — a $192/year gap purely from the compounding rule.
The amortization formula
Once you have the monthly rate r, the level payment P on principal L over n months is:
P = L × r × (1 + r)^n / ((1 + r)^n − 1)A worked example
Let's walk through a realistic scenario: a $650,000 home, 20% down ($130,000), 5.19% fixed rate, 25-year amortization.
- Loan principal: $520,000
- Annual rate: 5.19%
- Periods: 25 × 12 = 300 months
- Monthly rate: (1 + 0.0519/2)^(1/6) − 1 ≈ 0.0042799
- Monthly payment: ≈ $3,082
Why this matters for your wallet
Most online calculators outside Canada — and a surprising number inside Canada — use the American monthly-compounding formula. If you base your home-buying budget on the wrong number, you could plan around a payment that turns out to be $20–$30/month higher when you sit down with your lender. Over a 5-year term, that's real money.
What about CMHC insurance?
If your down payment is less than 20%, your lender adds a CMHC insurance premium to the loan. The premium becomes part of the principal and is amortized along with everything else. We cover the rules and tiers in our CMHC guide.
What about the stress test?
Federally regulated lenders must qualify you at the greater of your contract rate plus 2% or 5.25% — but you only pay your actual contract rate. The stress test affects how big a mortgage you can get, not your monthly payment once you have it.
Putting it all together
The full calculation is: take your purchase price, subtract your down payment, add CMHC insurance if it applies, convert your annual rate to a monthly rate using the right formula for your rate type, then plug everything into the amortization formula. Our calculator does all of this in real time, including provincial land transfer tax and the stress test.
