Almost nobody reads the interest section of a loan agreement. You see the monthly payment, you can afford it, you sign. Months later the balance has barely moved and you wonder where all that money went.
It went to interest — and once you see how loan interest is calculated, the whole thing stops feeling like a trick. The math behind a Canadian loan is simple. This guide walks through it in plain language, with real numbers, so you can look at any offer and know what it will actually cost before you sign.
What Loan Interest Actually Is
Interest is rent on money. A lender hands you a lump sum, and you pay for the time you keep it. The longer you hold it and the larger the balance, the more rent you pay.
Nearly every Canadian instalment loan — personal, car, consolidation — uses the same method: interest is charged on your outstanding balance, recalculated at every payment. If your loan is 12% per year and you pay monthly, the lender takes 1% (12 ÷ 12) of what you currently owe. That’s the interest portion of your payment. Whatever is left over reduces your principal.
This is why the balance moves slowly at first: early on, interest is calculated on a big number, so a bigger slice of each payment gets eaten. That one mechanic explains most of the confusion people have about their loans. And lenders can’t present it however they like — under the federal Interest Act, a contract quoting a rate for a period shorter than a year without stating the equivalent annual rate can only recover 5% per year. You’re entitled to see the annual number.
Simple vs Compound Interest
Simple interest is charged only on the original principal. Borrow $1,000 at 5% for five years and you owe $50 a year — $250 in total.
Compound interest is charged on the principal plus any interest already added. The same $1,000 at 5% compounded annually costs $276.28 over five years. Not dramatic at that size, but the gap widens fast with bigger balances, higher rates, and longer terms.
Here’s the part that trips people up: an instalment loan you pay on time isn’t really compounding against you. Your payment covers that period’s interest in full, so nothing is left to compound. Compounding only turns against you when interest goes unpaid — exactly what happens with revolving credit, which is why our credit card interest calculator guide shows minimum payments stretching into decades.
Mortgages are their own case. Section 6 of the Interest Act requires Canadian mortgages with blended payments to be quoted at a rate calculated half-yearly, not in advance. So a 5% mortgage compounds semi-annually for an effective annual rate of 5.0625% — a genuinely Canadian quirk.
Interest Rate vs APR — Why They Differ
The interest rate is the cost of the money. The annual percentage rate (APR) is that cost plus mandatory fees, expressed as one annual number. Federally regulated lenders must disclose it, along with the total cost of borrowing, under the Cost of Borrowing Regulations.
APR is the only number that lets you compare two offers honestly. A 9% loan with a $600 origination fee can easily cost more than an 11% loan with no fee. Compare rate to rate and you’ll pick wrong; compare APR to APR and the fees can’t hide.
There is a ceiling. Since 1 January 2025, the criminal rate under section 347 of the Criminal Code is an APR above 35% on most consumer loans — down from the old 60% effective annual rate. If a lender quotes more than 35% APR on an ordinary personal loan, something is wrong.
A Real $15,000 Loan, Month by Month
Say you borrow $15,000 over five years at 11.99%. Monthly rate: 11.99 ÷ 12 = 0.999%. First month’s interest: $149.88. Your payment is $333.59, so $183.72 goes to principal and the balance drops to $14,816.28. Next month interest is calculated on that smaller number, and so on for 60 months.
Two things stand out. Four percentage points on the same loan is a $1,771 difference — which is why it pays to know that loan interest rates are often negotiable. And an extra $100 a month cuts 17 months and over $1,500 off the total, because every extra dollar goes straight to principal and shrinks the base all future interest is calculated on.
If your current debts sit closer to the bottom row, that arithmetic is what makes consolidating at a lower rate worth a look — provided the new loan doesn’t stretch the term so far that you pay more overall.
What Determines Your Rate
Your rate is a base cost of money plus a risk premium for you specifically.
- The Bank of Canada policy rate. Held at 2.25% through the summer of 2026, it sets the floor lenders build on.
- Your credit score and history. The single biggest lever most borrowers control.
- Secured or unsecured. Collateral lowers the lender’s risk and your rate — the trade-off is covered in our guide to secured vs unsecured loans.
- Term length. Longer terms mean smaller payments but more total interest.
- The lender itself. Banks and credit unions price very differently from alternative lenders.
- Not the advertised “from” rate. Teaser rates go to the strongest applicants only.
- Not the monthly payment. A low payment usually means a longer term and more interest overall.
- Not the loan size alone. Borrowing more than you need costs you on every payment.
How to Check Any Loan Offer
- Find the APR, not the interest rate. It must be disclosed in writing. If you can’t find it, ask before you sign.
- Read the total cost of borrowing. The dollar figure you’ll hand over beyond the principal — the honest number.
- Divide the annual rate by 12. Multiply by the loan amount for your first month’s interest, then compare it to the payment. That ratio shows how fast the balance will move.
- Check the prepayment terms. Can you pay extra without penalty? Over five years that’s worth more than a small rate difference.
- Ask what’s optional. Loan insurance and add-ons are often presented as required. They rarely are.
If the numbers don’t work no matter how you run them, that’s information too — not a personal failure. When the payment isn’t affordable to begin with, our overview of how to choose a loan company in Canada and the alternatives to borrowing is a better next step than another application.
Not sure whether borrowing is the right move for your situation?
How do I calculate loan interest myself?
Divide your annual rate by the number of payments per year, then multiply by your current balance. On a $10,000 balance at 12% paid monthly: 12 ÷ 12 = 1%, and 1% of $10,000 is $100 of interest this month. Subtract that from your payment to see how much is reducing principal, then repeat with the new balance.
Why is so much of my early payment going to interest?
Because interest is charged on your outstanding balance, and that balance is largest at the start. On a $15,000 loan at 11.99%, the first payment is about 45% interest; by the final year it’s almost entirely principal. Nothing is wrong with your loan — this is how amortization works.
What’s the difference between the interest rate and the APR?
The interest rate covers only the cost of the money borrowed. The APR adds mandatory fees — origination, administration, brokerage — as one annual figure. Because fees are baked in, APR is the only fair way to compare two loans, and federally regulated lenders must disclose it before you sign.
Does paying extra actually save me money?
Yes, more than most people expect. Extra payments go entirely to principal, shrinking the balance every future interest calculation is based on. On a $15,000 loan at 11.99% over five years, an extra $100 a month clears it 17 months early and saves about $1,518. Check that your agreement allows prepayment without penalty.
Is there a legal limit on loan interest in Canada?
Yes. Since 1 January 2025, section 347 of the Criminal Code sets the criminal rate at an APR above 35% for most consumer loans, replacing the old 60% effective annual rate. Narrow exemptions exist for small pawn loans and some commercial lending, but on an ordinary personal loan, anything above 35% APR should stop you cold.
After 20 years of structuring multi-million dollar corporate debt facilities and corporate turnarounds in investment banking, Marcus now leads Canadian Debt Relief to apply those exact same balance-sheet optimization frameworks to Canadian household debt.
