How to Use a Mortgage Calculator (and Read an Amortization Schedule)
A mortgage calculator turns four numbers into a payment. Used well, it also shows you how much of that payment is interest, how fast you're building equity, and what a small change — a different payment frequency, a lump sum, five fewer years — is worth. Here's how to get real answers out of one, with Canadian numbers.
Key takeaways
- A mortgage calculator needs four inputs: the amount, the rate, the amortization and the payment frequency.
- Canadian fixed-rate mortgages compound semi-annually, so use a Canadian calculator — an American one overstates the payment.
- An amortization schedule shows that early payments are mostly interest; that's when extra payments do the most good.
- Accelerated bi-weekly payments and annual prepayments can take years off a mortgage.
The four inputs
| Input | What to enter |
|---|---|
| Mortgage amount | Purchase price minus down payment — plus the mortgage insurance premium if you're putting down less than 20%. |
| Interest rate | The rate you've been quoted, not the posted rate. If you're testing affordability, also try the stress-test rate. |
| Amortization | The total time to pay the mortgage off: usually 25 years, up to 30 for many uninsured mortgages and for insured first-time buyers and new builds. |
| Payment frequency | Monthly, semi-monthly, bi-weekly, weekly — or the accelerated versions. |
Don't confuse amortization with term. The term is how long your rate and contract last — often five years. The amortization is how long the whole debt takes to repay. You'll renew several times within one amortization.
Why a Canadian mortgage calculator gives a different answer
Canadian fixed-rate mortgages are compounded semi-annually, not monthly — a consequence of the federal Interest Act. At the same quoted rate, that makes the Canadian payment slightly lower. If an online mortgage calculator is built for the U.S. market and compounds monthly, it will overstate a Canadian payment by a few dollars a month, which adds up over 25 years.
Our mortgage payment calculator uses Canadian semi-annual compounding.
A worked example
Take a $500,000 mortgage at 5.00% fixed, amortized over 25 years, paid monthly.
- Monthly payment: $2,908.02
- Interest paid in the first year: about $24,510
- Principal paid in the first year: about $10,386
- Total interest over 25 years, if the rate never changed: about $372,407
Stretch the same mortgage to 30 years and the payment falls to $2,668.45 — but total interest rises to about $460,643. A longer amortization buys cash flow, and you pay for it.
How to read an amortization schedule
An amortization schedule lists every payment, split into interest and principal, with the balance left after each one. Three things to look for:
- The interest share at the start. In the example above, about 70% of the first year's payments go to interest. Equity builds slowly at first.
- The crossover point. Partway through, principal overtakes interest in each payment. The lower your rate or the shorter the amortization, the sooner that happens.
- The balance at renewal. Look at what you'll still owe at the end of your term. That's the amount you'll renew or refinance — and what your next rate will apply to.
Any good mortgage amortization calculator will produce the full schedule; ours shows the balance year by year.
Payment frequency: what actually saves money
| Frequency | Payment on the example | Paid off in |
|---|---|---|
| Monthly | $2,908.02 | 25 years |
| Regular bi-weekly | $1,342.17 | about 25 years |
| Accelerated bi-weekly | $1,454.01 | about 21.5 years |
Regular bi-weekly simply spreads the same annual amount over 26 payments, so it saves very little. Accelerated bi-weekly pays half the monthly amount every two weeks — 26 half-payments, or the equivalent of 13 monthly payments a year. That extra month goes straight to principal, which in this example clears the mortgage about three and a half years early and saves roughly $60,000 of interest.
Prepayments: the biggest lever you control
Most closed mortgages let you prepay a percentage of the original amount each year — often 10% to 20% — without penalty. Using the example, a $10,000 lump sum at the end of each year would pay off the mortgage in about 16.5 years and cut total interest to roughly $233,800. A mortgage payoff calculator or mortgage prepayment calculator will show the effect of your own numbers.
Check your prepayment privileges before you sign; they vary widely between lenders and matter more than most people realise. Fixed vs variable covers what it costs to repay more than your privileges allow.
Other calculators worth using
- Mortgage renewal calculator — what your payment does at renewal.
- Mortgage refinance calculator — how much equity you can access and what it costs.
- How much mortgage can I afford? — the affordability rules lenders apply.
- CMHC mortgage insurance — the premium that's added to your mortgage when you put down less than 20%.
Sources
This article is general information, not financial advice. Examples assume a constant rate and are rounded. Your payment, prepayment privileges and amortization options depend on your lender and mortgage. Mortgage financing is subject to lender approval.
Frequently asked questions
One that compounds fixed rates semi-annually, lets you enter the insurance premium, and shows a full amortization schedule. Check that it's built for Canadian mortgages before trusting the payment.
A mortgage calculator gives the payment. An amortization calculator also shows how each payment splits between interest and principal over time, and the balance remaining at any point.
Most give principal and interest only. Lenders add property tax and heating (and half of condo fees) when they check affordability, so budget for those separately.
Look at the amortization schedule at the end of your term — for a five-year term, the balance after payment 60. That's the amount your renewal rate will apply to.
For most borrowers, yes. It adds the equivalent of one monthly payment a year, all of it to principal, which shortens the amortization by several years without needing a lump sum.
Run the numbers with someone who does this daily
We'll model your payment, renewal balance and prepayment strategy across several lenders' products.