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Why Canadian Mortgages Aren't Just a US Mortgage in Different Currency
Canadian mortgages have a legal and mathematical quirk that catches a lot of people off guard: by federal law, fixed-rate mortgages must be compounded semi-annually, not monthly, no matter how often you actually make payments. That single rule is the entire reason this calculator exists as its own tool rather than a re-skin of a US mortgage calculator.
Semi-Annual Compounding Is the Law
Canada's Interest Act requires fixed-rate mortgages to compound at most semi-annually. Your quoted nominal annual rate gets converted into an effective monthly rate via (1 + rate/2)^(2/12) - 1, not simply divided by 12 like in the US.
Amortization vs. Term
The amortization period (often 25 years) is how long it would take to fully pay off the mortgage. The term (often 5 years) is how long your current rate is locked in before you must renew or renegotiate — usually several times over the life of the mortgage.
Renewal Is Not Payoff
Unlike a US mortgage that runs to zero on a single fixed rate for its whole life, a Canadian mortgage hits a renewal checkpoint at the end of every term, where you negotiate a new rate against whatever balance is left — which is usually still substantial.
Rate Risk at Renewal
Because your rate only locks in for the term, not the whole amortization, rising rates at renewal can meaningfully increase your payment on the remaining balance — planning for that remaining balance ahead of time matters.
Worked Example
A $400,000 mortgage at 5.5%, amortized over 25 years, with a 5-year term:
- Monthly payment: approximately $2,441.57.
- Total interest over the full 25-year amortization: approximately $332,468.33.
- Balance remaining at the end of the 5-year term: approximately $356,749.71 — still over 89% of the original loan, since amortization schedules are heavily interest-weighted in the early years.
For comparison, the same $400,000 at 5.5% over 300 months using US-style monthly compounding would pay about $2,456.35 per month — slightly higher, because semi-annual compounding produces a marginally lower effective monthly rate than simple monthly compounding at the same nominal annual rate.
25-Year Amortization Snapshot
- Monthly payment: $2,441.57
- Total interest (25 yr): $332,468.33
- Balance at 5-yr renewal: $356,749.71
Why the Remaining Balance Matters More Than the Full Schedule
Most borrowers never actually experience the full amortization schedule at a single rate — they renew every term, often at a different rate. That makes the "balance remaining at end of term" figure far more practically useful for a Canadian borrower than the theoretical total interest over 25 years, since it's the number you'll actually be renegotiating against at your next renewal.
A note on this calculator: if you enter a term equal to or longer than your amortization, the mortgage is treated as fully paid off by the end of that period, and the remaining balance is shown as zero.
Key Takeaways
- Semi-Annual Compounding Is Mandatory: Canadian law requires this compounding convention for fixed-rate mortgages — it's not optional or lender-specific.
- Term ≠ Amortization: Your rate is only locked for the term; the amortization is the full theoretical payoff horizon. Don't confuse the two when reading mortgage offers.
- Plan for Renewal: The remaining balance at term's end is what you'll actually be negotiating a new rate against — know that number well before your renewal date arrives.
- Early Years Are Interest-Heavy: A large chunk of your balance can remain even after a full 5-year term, since early payments are weighted heavily toward interest.