If you've ever tried to calculate your Canadian mortgage payment using a standard formula and gotten a slightly different number than your bank — this is why. Canadian mortgages compound semi-annually by law, not monthly like most other loans and like virtually all American mortgages. The difference is small per payment, but over a 25-year amortization it adds up to thousands of dollars.
Our mortgage payment calculator uses the correct Canadian semi-annual compounding formula — the same one your bank uses. Enter your rate and see your exact payment.
What is compounding frequency?
When a lender quotes you a mortgage rate of 5%, they mean the interest compounds — is calculated and applied — at some frequency. The more frequently it compounds, the more you actually pay over a year.
- Monthly compounding: interest calculated and added to balance 12 times per year (common in the US and for most Canadian non-mortgage loans)
- Semi-annual compounding: interest calculated and added to balance only 2 times per year (required for all Canadian residential mortgages by the Interest Act)
- Annual compounding: interest calculated once per year (GICs and some bonds)
Semi-annual compounding is actually slightly less expensive than monthly compounding at the same stated rate, because the interest compounds less frequently. A 5.00% rate compounded semi-annually is equivalent to a 5.063% effective annual rate, while 5.00% compounded monthly is 5.116% effective.
The Canadian mortgage formula step by step
Here's exactly how Canadian lenders convert a quoted rate to a monthly payment rate:
Step 1: Find the semi-annual rate
Divide your annual rate by 2. At 5.00%: 5.00% ÷ 2 = 2.50% per semi-annual period
Step 2: Convert to an effective annual rate
Compound that semi-annual rate to get the effective annual equivalent: (1 + 0.025)² − 1 = 5.0625% effective annual rate
Step 3: Convert to a monthly rate
Take the 12th root of (1 + effective annual rate): (1 + 0.050625)^(1/12) − 1 = 0.41246% per month
Step 4: Apply to your mortgage balance
Use the standard amortization formula with this monthly rate. For a $500,000 mortgage over 25 years (300 months): Payment = $500,000 × [0.004125 × (1.004125)^300] ÷ [(1.004125)^300 − 1] = ~$2,908/month
| Compounding Method | Monthly Rate Used | Monthly Payment on $500K, 25yr, 5% | Total Interest Paid |
|---|---|---|---|
| Semi-annual (Canadian) | 0.41246% | $2,908 | $372,400 |
| Monthly (US/other loans) | 0.41667% | $2,922 | $376,600 |
| Difference | — | $14/month | $4,200 over 25 years |
The $14/month difference seems small, but it adds up to over $4,200 in savings over a 25-year amortization. More importantly, using the wrong formula when calculating your own affordability could throw your estimates off enough to matter.
Why does Canada use semi-annual compounding?
It's required by the Interest Act of Canada, a federal law that prohibits lenders from charging compound interest on mortgages more than semi-annually. The law was designed to protect borrowers from aggressive compounding by lenders. The practical result is that Canadian mortgage math is unique — and a lot of online calculators built for American audiences get it wrong.
Generic mortgage calculators (including those built into many bank websites and most American financial tools) often use monthly compounding. This produces a slightly higher payment than the actual Canadian calculation. Our calculator uses the legally correct Canadian semi-annual formula — the same one your lender uses.
Does this affect your mortgage rate comparisons?
Yes — when comparing mortgage rates from different lenders, you should compare the effective annual rate (EAR), not just the stated nominal rate, especially if comparing mortgage rates to other investment rates. A 5.00% mortgage rate compounded semi-annually has an EAR of 5.0625%. A savings account paying 5.00% compounded monthly has an EAR of 5.116%.
For most practical purposes — shopping for mortgages and comparing lenders — all Canadian lenders use the same semi-annual compounding convention, so direct rate comparisons are still valid. The formula issue mainly matters when you're trying to calculate your own payments or build your own amortization table.
Calculate your payment with the correct Canadian formula
Our mortgage calculator uses semi-annual compounding as required by the Interest Act — giving you the same number your bank will quote.
→ Calculate My Mortgage PaymentFrequently asked questions
Why do Canadian mortgages compound semi-annually?
The Interest Act of Canada requires it. The law prohibits mortgage lenders from compounding interest more than twice per year. This makes Canadian mortgage math slightly different from American mortgages (monthly compounding) and most other Canadian loans.
Does semi-annual compounding make my mortgage cheaper?
Yes, slightly — compared to monthly compounding at the same stated rate. A 5.00% semi-annual rate results in lower payments than a 5.00% monthly rate. The difference is small (roughly $14/month on a $500,000 mortgage) but adds up over a 25-year amortization.
Why does my bank's calculator give a different answer than other calculators?
Most generic mortgage calculators online use monthly compounding (the US standard). Canadian bank calculators and our calculator use semi-annual compounding as required by Canadian law. The bank's number is correct for your actual mortgage payment.
Does this apply to all Canadian mortgages?
Yes — all residential mortgages in Canada are subject to the Interest Act and must use semi-annual compounding (or less frequent). This applies regardless of whether your mortgage has a fixed or variable rate, and regardless of your payment frequency (monthly, bi-weekly, weekly).