Canadian Mortgage Calculator: Monthly Payment, Amortization and Affordability
Understanding how Canadian mortgage payments are calculated — and how amortization period, down payment and the stress test interact — is the foundation of an accurate home buying budget. This guide explains the math, the rules and how to use RealMaster's mortgage calculator to plan your purchase.
How Canadian mortgage payments are calculated
A Canadian mortgage payment is calculated using the standard amortizing loan formula. Because Canadian mortgages compound semi-annually (not monthly like U.S. mortgages), there is an important conversion step before applying the monthly payment formula.
The formula
Given an annual interest rate r, amortization of n months and principal P:
- Convert the annual rate to a monthly equivalent accounting for semi-annual compounding:
monthly_rate = (1 + r/2)^(1/6) − 1 - Apply the standard annuity formula:
payment = P × monthly_rate × (1 + monthly_rate)^n / ((1 + monthly_rate)^n − 1)
Example: $600,000 mortgage, 5.00% annual rate, 25-year amortization (300 months).
- Monthly rate = (1 + 0.05/2)^(1/6) − 1 = 0.41239%
- Monthly payment = $600,000 × 0.0041239 × (1.0041239)^300 / ((1.0041239)^300 − 1)
- Result: approximately $3,490/month
The difference between Canadian semi-annual compounding and simple monthly compounding is small (a few dollars per month) but adds up over the amortization period. Most online calculators handle this automatically — but verify any third-party calculator specifies Canadian compounding if precision matters.
Principal vs. interest breakdown over time
In the early years of a mortgage, most of each payment goes toward interest. Over time, the interest portion decreases and the principal portion increases — this is the nature of an amortizing loan. After 5 years on a 25-year, $600,000 mortgage at 5%, you will have paid approximately $57,000 in principal and $150,000 in interest, leaving a remaining balance around $543,000. RealMaster's amortization table view shows this breakdown year by year.
Canadian mortgage rules you need to know
Insured mortgages: 25-year maximum amortization
If your down payment is less than 20% (an "insured" or "high-ratio" mortgage), the maximum amortization period is 25 years under standard CMHC rules. Starting in 2024, first-time buyers purchasing new construction can access 30-year amortization on insured mortgages — confirm current rules with your mortgage broker as policies evolve.
Uninsured mortgages: 30-year maximum amortization
With 20% or more down (a "conventional" or "uninsured" mortgage), lenders can offer amortization periods up to 30 years. A longer amortization reduces monthly payments but significantly increases total interest paid over the life of the loan. The difference in total interest between 25-year and 30-year amortization on a $700,000 mortgage at 5% is approximately $100,000.
Mortgage terms (not amortization)
The mortgage term is separate from amortization. Most Canadian mortgages have a 5-year term — meaning the rate and conditions are set for 5 years, after which you renew at prevailing rates. At the end of your term, your mortgage balance (not the full original amount) is renewed. Shorter terms (1–3 years) offer flexibility to catch rate drops; longer terms (5–10 years) provide payment certainty.
Prepayment privileges
Most Canadian mortgages include prepayment privileges: the right to increase your regular payments (typically up to 20% per year) or make lump-sum prepayments (typically up to 20% of the original mortgage annually) without penalty. Using prepayment privileges aggressively can reduce your amortization by years. Open mortgages allow full prepayment at any time but carry higher rates.
How to use the RealMaster mortgage calculator
The RealMaster mortgage calculator on RealMaster.com is designed specifically for Canadian mortgage math. Here is how to get the most accurate estimate:
- Enter the purchase price of the home you are evaluating
- Enter your down payment amount — the calculator will show whether CMHC insurance applies and calculate the premium automatically
- Enter the interest rate — use your actual quoted rate for payment planning, or use the stress test rate (5.25% or contract +2%) for qualifying calculation
- Select amortization period — 25 years for insured, up to 30 for conventional
- Review the output: monthly payment, bi-weekly payment, total interest over the term, amortization table and CMHC premium if applicable
The calculator also shows total cost of ownership when you add property tax (automatically estimated from the property's location), condo maintenance fees and home insurance — giving you a true monthly carrying cost figure rather than just the mortgage payment.
Affordability: what can I actually borrow?
Canadian lenders use two debt ratios to determine maximum mortgage size:
- GDS (Gross Debt Service ratio): mortgage payment + property taxes + heating + 50% of condo fees must be no more than 32%–39% of gross household income
- TDS (Total Debt Service ratio): all of the above plus all other debt payments (car loans, student loans, credit card minimums) must be no more than 44% of gross household income
Both ratios are calculated using the stress test qualifying rate, not your actual contract rate. RealMaster's affordability calculator works backward from your income and debts to show your maximum qualifying purchase price under current stress test conditions.
Frequently asked questions
Why do Canadian mortgages compound semi-annually instead of monthly?
Canadian mortgage interest compounding is regulated by the Interest Act (Canada), which limits mortgage compounding to a maximum of semi-annual frequency. This differs from U.S. mortgages, which compound monthly. Semi-annual compounding results in a slightly lower effective annual rate than monthly compounding at the same nominal rate — meaning Canadian borrowers pay slightly less interest than a comparable U.S. borrower at the same quoted rate. The difference is small but matters for precise payment calculations.
What is the difference between a 25-year and 30-year amortization?
A 30-year amortization reduces your monthly payment by approximately 10%–12% compared to a 25-year amortization at the same rate and principal. However, the total interest paid over the life of the loan is substantially higher. On a $600,000 mortgage at 5.00%, the difference in total interest between 25-year and 30-year amortization is roughly $80,000–$100,000. Many buyers use a 30-year amortization to reduce monthly cash flow pressure, then make prepayments to reduce the effective amortization period.
Should I choose a fixed or variable rate mortgage in 2025?
This depends on your risk tolerance and rate outlook. Variable rates move with the Bank of Canada's overnight rate — if you expect rates to continue falling, variable rates allow you to benefit without breaking your mortgage. Fixed rates provide certainty for the term. As of mid-2025, both options have compelling arguments. A mortgage broker can compare specific product offerings from multiple lenders and model scenarios for your situation. The RealMaster calculator supports both rate types.
How much does my monthly payment change if interest rates go up 1%?
On a $600,000 mortgage at 25-year amortization, a 1% increase in your interest rate (e.g., from 5.0% to 6.0%) increases your monthly payment by approximately $320–$350/month. Over the 5-year term, this adds up to roughly $20,000 in additional interest. This sensitivity is why the B-20 stress test requires qualifying at rate plus 2% — to ensure borrowers can absorb a significant rate increase at renewal.
Can I include CMHC insurance in the RealMaster mortgage calculator?
Yes. When you enter a down payment of less than 20%, the RealMaster calculator automatically calculates the applicable CMHC premium (4.0%, 3.1% or 2.8% depending on down payment percentage), adds it to the mortgage principal and recalculates the monthly payment on the insured mortgage amount. The PST/HST payable on the premium (if applicable in your province) is shown separately as a closing cost item.