Fixed vs variable mortgage on a first purchase

Mortgages · 7 min read

Most fixed-versus-variable advice is a disguised interest-rate forecast: variable wins if rates fall, fixed wins if they rise, and nobody knows. For a first purchase there is a better way to decide. Price three things on your actual loan amount — the payment if rates move against you, the penalty if you have to break the mortgage early, and the headroom left in a first-year homeowner budget that has not yet met a furnace repair. Those numbers, not a prediction, tell you which risk you can afford.

The two machines that set your rate

A variable mortgage rate is priced off the lender's prime rate, which tracks the Bank of Canada's overnight rate. When the Bank moves, prime moves, and a variable rate follows — usually within days. A fixed mortgage rate works differently: it is priced off Government of Canada bond yields, especially the five-year yield, which reflect what markets expect to happen next. That is why fixed and variable rates can move in opposite directions: the Bank of Canada can hold its rate steady while bond yields climb and fixed offers get more expensive, or bond yields can fall in anticipation of a cut before prime moves at all.

The structure matters as much as the label. With a fixed-rate mortgage, the rate is set for the entire term and the payment does not change. With a variable-rate mortgage, the rate can change during the term — but the payment behaviour depends on the product. Some variable mortgages have adjustable payments: the payment itself rises and falls with prime. Others have fixed payments: the payment stays the same and the split between interest and principal changes instead. Those two variable products carry very different risks, and treating them as one thing is the most common mistake in comparison guides.

One mortgage, three futures: the payment-shock table

Take a $500,000 mortgage on a 25-year amortization. The rates below are worked examples for illustration — not quotes, and not a market snapshot; a lender's actual offers change and depend on the file. Payments are computed the Canadian way, with semi-annual compounding converted to a monthly rate.

Read the table as a budget test, not a forecast. The question is not whether a two-point rise is likely; it is whether the household can carry a $562-a-month increase in year one or two of owning a home, when the emergency fund has just been spent on a down payment and closing costs. Note also the last column: a higher rate does not just cost more each month, it slows principal repayment, so the balance after a five-year term is about $14,226 higher in the two-point-rise case than at the starting rate. A fixed rate at 4.25% costs $135 a month more than the starting variable example — and buys complete certainty about which of those rows the household will actually live in.

The penalty difference nobody prices before signing

First homes are often not long homes: jobs move, households grow, relationships change. If a closed mortgage is broken early — by selling, refinancing, or switching lenders before the term ends — the lender may charge a prepayment penalty. The Financial Consumer Agency of Canada (FCAC) notes that penalties can apply when a borrower pays off a mortgage early, including on a home sale, transfers to another lender, or exceeds the prepayment privileges in the agreement. Open mortgages allow early payoff without that penalty but are a different, usually shorter and higher-priced, product.

The calculation method is where fixed and variable genuinely diverge. FCAC explains that prepayment penalties are usually the greater of three months' interest or the interest rate differential (IRD) — the difference between the contract rate and a current rate for the remaining term, applied to the balance over the time left. On the example $500,000 mortgage:

The IRD row is a simplified illustration, not a lender quote: FCAC warns that the differential is often based on posted rates, that the actual formula is in the mortgage agreement, and that penalties are frequently larger than consumers expect — it has cited a reported case of approximately $30,000. The practical lesson survives the simplification. A variable penalty is roughly knowable in advance (three months' interest on the balance). A fixed penalty is knowable only in the worst direction: it grows precisely when rates have fallen, which is exactly when refinancing looks attractive. A buyer who already suspects a move or a refinance within the term should weigh that asymmetry heavily.

Fixed-payment variable and the trigger rate

The fixed-payment variable mortgage deserves its own section because its risk is quiet. The payment never changes, which feels like a fixed mortgage — until rates rise enough that the whole payment is consumed by interest. That threshold is the trigger rate: the rate at which the regular payment covers interest only and no principal at all. FCAC and the Office of the Superintendent of Financial Institutions describe what happens next: the lender may require the borrower to increase payments, make extra payments to cover the excess interest, or convert to a fixed rate. Past the related trigger point — where the growing balance exceeds the lender's acceptable ratio to the property value — adjustment is no longer optional, because unpaid interest has been added to the principal and the borrower is paying interest on interest.

None of that makes the product unusable. It means a buyer choosing it should know two numbers before signing: the trigger rate in the agreement (federally regulated lenders must disclose it for fixed-payment variable mortgages), and the payment increase the household could accept if the lender requires one. If either number is a surprise after closing, the mortgage was chosen on its starting payment alone — the same error as choosing any variable product without the shock table above.

A decision framework based on headroom, not forecasts

• Run the +2 row first. Compute the payment at the starting variable rate plus two points. If that payment breaks the monthly budget, the variable choice is already made: take fixed, or buy a cheaper home. The stress test uses the same two-point logic for a reason.
• Count the break risk honestly. Any realistic chance of selling, refinancing, or breaking within the term favours variable's three-months'-interest penalty over fixed IRD exposure — or a shorter fixed term, which shrinks the years an IRD can span.
• Separate the two variable products. Adjustable payments make rate moves visible immediately; fixed payments hide them in the amortization until the trigger rate. Choose consciously, and get the trigger rate in writing.
• Protect the first-year reserve. FCAC's own guidance puts the monthly budget at the centre of choosing a mortgage. A first purchase with a thin post-closing reserve argues for payment certainty even at a modest premium — the $135-a-month difference in the table is, in effect, an insurance price.
• Consider the middle options. A one-to-three-year fixed term trades a sooner renewal decision for certainty now; a hybrid or split mortgage puts part of the loan on each side. Both are compromises, and both beat guessing.

The framework deliberately contains no view on where rates go next. A first-time buyer cannot control the Bank of Canada or the bond market. What can be controlled is the size of the loan, the reserve left after closing, and whether the mortgage's worst plausible row still fits the budget. Choose the product whose worst row is survivable, and the forecast stops mattering very much.

FAQ

Is variable always cheaper over a full term? No. It is cheaper in the periods when rates fall or hold, and more expensive when they rise — the table above shows both directions on the same loan. Any claim that one side always wins is a forecast dressed as a fact.

Can a variable mortgage be converted to fixed mid-term? Many lenders offer a conversion option, typically into a fixed rate the lender offers at that time, but the terms are product-specific. It is a question to ask before signing, along with the trigger rate and the exact prepayment privileges.

Why did a fixed offer change when the Bank of Canada did nothing? Because fixed rates follow Government of Canada bond yields, not the overnight rate. Bond markets move on expectations, so fixed offers can rise or fall between Bank of Canada announcements.

General information only, not financial advice. Worked examples use illustrative rates and simplified penalty arithmetic, not lender quotes; actual penalties, trigger rates, and prepayment privileges are set out in your mortgage agreement — confirm them with your lender or a licensed mortgage broker before signing.