A mortgage quoted at 5 percent in Canada is technically a 5.0625 percent loan, and the gap between those two numbers exists because of a rule buried in federal law that most borrowers never hear explained in plain language. Section 6 of Canada’s Interest Act requires that a residential mortgage’s stated interest rate be calculated yearly or half-yearly, not in advance, and in practice virtually every fixed-rate mortgage in the country compounds semi-annually as a result. That single rule shapes your entire amortization schedule, and understanding it is the difference between a rough guess at your mortgage costs and actually knowing them.
An amortization schedule is the month-by-month breakdown of exactly how each payment splits between interest and principal over the life of your loan, and it behaves in ways that surprise a lot of homeowners the first time they actually look at one closely.
Amortization and term are two different clocks
Before the schedule itself makes sense, the distinction between amortization and term has to be clear, since conflating the two is one of the most common mistakes in how people talk about their mortgage. Your amortization period is the total length of time it would take to pay off the entire mortgage, commonly 25 years, sometimes 30 for eligible insured buyers. Your term is the length of a single contract with your current rate and lender, commonly five years, after which you renew into a new term at whatever rate is on offer, while the amortization clock just keeps running underneath.
A 25-year amortization doesn’t reset every time you renew. If you’re two years into a five-year term on a 25-year amortization, you have 23 years of amortization remaining when that term ends, not a fresh 25. Our guide to mortgage renewal covers what actually happens at that renewal point, and how it interacts with whichever fixed or variable rate you renew into, but the amortization schedule itself is what determines how much of your balance is left to renew against in the first place.
The semi-annual compounding rule, explained properly
Here’s what that Interest Act rule actually does mathematically. A nominal rate of 5 percent, compounded semi-annually, works out to 2.5 percent every six months, and because that 2.5 percent compounds on itself, the true annual cost comes to 5.0625 percent, not a flat 5. Compare that to how mortgages work in the United States, where monthly compounding on the same nominal 5 percent rate produces an effective annual rate of 5.116 percent instead. The Canadian rule genuinely works in the borrower’s favour, producing a lower true cost than more frequent compounding would, even though the number on your mortgage paperwork looks identical either way.
Where this matters practically is converting that semi-annual rate into the monthly rate your actual payment gets calculated against, since almost everyone pays monthly while the compounding itself only happens twice a year. The formula lenders use takes your annual rate, divides it by two to get the semi-annual rate, and then converts that into an equivalent monthly rate mathematically rather than just dividing by twelve. Any legitimate Canadian mortgage calculator applies this conversion automatically, but it’s worth knowing it’s happening, since a US-based calculator or a simple spreadsheet formula that divides your rate by twelve directly will give you a slightly wrong number every time.
What the schedule actually looks like month to month
Take a genuinely worked example, a $450,000 mortgage at 4.5 percent on a 25-year amortization, which produces a monthly payment of $2,490.63 once the semi-annual compounding is applied correctly. In the very first month, $1,671.89 of that payment goes to interest and only $818.73 chips away at principal, a split that feels discouraging if you’re not expecting it. That’s not a bad deal, it’s simply how amortization works. Interest is charged on your current outstanding balance, and in month one your balance is still the full $450,000, so the interest portion is unavoidably large.
By month 60, five years in, the split has shifted meaningfully, with $1,471.65 going to interest and $1,018.98 to principal. The real turning point, where more of your payment finally goes toward principal than interest, arrives around month 115, roughly nine and a half years into a 25-year amortization, noticeably earlier than the halfway point most people assume. By month 150, twelve and a half years in, principal has pulled well ahead at $1,422.71 against $1,067.92 in interest. By the final month of the schedule, interest has shrunk to a token $9.22 while the remaining $2,481.41 clears the balance entirely.
Twenty-five years versus thirty, in real dollars
The choice between a 25-year and 30-year amortization is one of the most consequential decisions in the entire mortgage process, and running the actual numbers side by side makes the tradeoff concrete rather than abstract, a decision worth checking against your own affordability numbers before committing either way. On that same $450,000 mortgage at 4.5 percent, stretching to a 30-year amortization drops the monthly payment to $2,268.97, a saving of $221.66 every month compared to the 25-year schedule. That’s real, immediate breathing room in a monthly budget, and 30-year amortizations exist specifically as an option for eligible first-time buyers and new-build purchasers on insured mortgages, not as a universal choice available to every borrower.
The cost of that breathing room shows up over the full life of the loan. The 25-year schedule totals $297,188.49 in interest paid over its life. The 30-year schedule totals $366,829.20, a difference of $69,640.71 in extra interest for the same borrowed amount at the same rate. Neither choice is objectively wrong, a tighter monthly budget genuinely benefits from the 30-year payment, but the true cost of that flexibility is nearly $70,000 on this example alone, and that number deserves to be part of the decision rather than something discovered years later.
How extra payments actually reshape the schedule
This is where prepayment privileges earn their keep, and where the shape of the schedule works strongly in your favour if you use them. Because interest is calculated on your outstanding balance each period, any extra payment that reduces principal early in the schedule saves interest for every single month remaining on the loan, not just the month the extra payment was made. A lump sum applied in year one is worth meaningfully more than the same lump sum applied in year twenty, simply because it has more months left to keep compounding savings on your behalf.
Most Canadian closed mortgages allow an annual lump-sum prepayment and a payment-increase option, and running even a modest extra contribution through a proper amortization calculator, rather than guessing at the impact, is the clearest way to see exactly how many months or years it shaves off your specific schedule, an approach our full breakdown of mortgage financing in Canada covers alongside the other prepayment mechanics worth knowing. The effect compounds with the size of your mortgage and the number of years remaining, which is part of why prepaying early in a mortgage’s life tends to deliver more total savings than the identical dollar amount paid later.
Building your own schedule with confidence
Confirm whether your specific mortgage compounds semi-annually or, if it’s variable, potentially monthly, since that single detail changes every number in your schedule and not every calculator applies it correctly by default. Run your actual balance, rate, and remaining amortization through a mortgage calculator that explicitly states it uses Canadian semi-annual compounding rather than a generic or US-based tool, and cross-check the rate itself against current Canadian mortgage rates so the number feeding into your schedule is accurate to begin with. Compare the 25-year and 30-year versions of your own numbers side by side rather than defaulting to whichever one a lender mentions first, and if you have room in your budget for even a modest annual lump sum, model that against your own schedule specifically, since the earlier that extra payment lands, the more it’s actually worth over the life of the loan.
