A couple earning a combined $95,000 a year sits down and pictures a $500,000 budget. It feels reasonable against their income, their rent, their sense of what “affordable” should mean. Then a lender runs the actual numbers and comes back closer to $410,000. Nobody made a mistake here. The couple just didn’t know which math the bank was going to use, and that gap between the number people picture and the number a lender approves is where most house hunts go sideways before they even start.
Mortgage affordability in Canada is calculated using two debt ratios, not a simple multiple of your income. Lenders cap your housing costs at 39 percent of your gross monthly income (the GDS ratio) and your total debt payments, housing included, at 44 percent (the TDS ratio). Add a mandatory stress test on top of that, and the number your income “should” support and the number a lender will actually approve can differ by tens of thousands of dollars.
The two ratios that actually decide your number
Gross Debt Service, or GDS, measures your housing costs against your gross monthly income before taxes. Housing costs here means more than just the mortgage payment. It includes principal and interest, property tax, heating costs, and half of any condo fees if you’re buying a unit with fees attached. CMHC’s own underwriting guidelines cap this ratio at 39 percent for insured mortgages, the ones with less than 20 percent down.
Total Debt Service, or TDS, takes that same housing number and adds every other debt payment you’re carrying, car loans, credit card minimums, student loans, any line of credit balance. That combined figure gets capped at 44 percent of your gross income for insured mortgages. If you’re debt-free apart from the mortgage, GDS and TDS end up close to identical. Carry a car payment and a credit card balance, though, and TDS can become the tighter constraint even when your housing costs alone look comfortable.
Here’s where the couple from the opening actually lands. On a combined $95,000 income, their gross monthly income works out to roughly $7,917, which puts their GDS ceiling at $3,088 a month for housing. Subtract a realistic $300 in property tax and $100 in heating costs, and they’re left with about $2,688 available for principal and interest. That’s the number that determines what they can actually borrow, not their income directly.
The stress test that shrinks the number further
Even after the GDS math, one more hurdle stands between that $2,688 monthly budget and the mortgage amount it translates into. Federally regulated lenders have to qualify you at a stress-tested rate, the higher of your actual contract rate plus 2 percentage points, or a 5.25 percent floor set by federal regulation. That floor has held steady since 2021, and it’s the rate your affordability gets calculated against, not the rate you’ll actually pay.
Take a contract rate of 4.19 percent, a realistic insured five-year fixed rate as of mid-2026, against a national average home price that sat at $696,078 in June 2026. The stress rate on that mortgage works out to 6.19 percent. Run the couple’s $2,688 monthly budget through a 25-year amortization at that stress rate, and it supports a mortgage of roughly $412,700, not the $500,000 sticker price they had in mind. Their actual monthly payment at the real 4.19 percent rate on that same mortgage would only be about $2,214, well under their ceiling, but the lender doesn’t qualify you on the rate you’ll pay. It qualifies you on the rate you’d be paying if rates rose two full points from here.
How your down payment changes the price you can actually offer
The mortgage amount from the stress test isn’t your total budget. Add whatever you’ve saved for a down payment, and Canada’s tiered minimum down payment rules determine how large a purchase price that combination can actually support. The minimum is 5 percent on the first $500,000 of the purchase price and 10 percent on any portion between $500,000 and $1.5 million. Effective December 15, 2024, that $1.5 million threshold applies to all high-ratio borrowers, not just first-time buyers, and homes priced at or above that mark require a full 20 percent down with no default insurance available at all.
Back to the couple. If they’ve saved $50,000 for a down payment and their mortgage qualifies at $412,700, their total purchase price ceiling lands around $462,700, comfortably clearing the 5 percent minimum on a home in that range with room to spare. Worth knowing separately, a 30-year amortization (instead of the standard 25) is available on insured mortgages, but only for first-time buyers and buyers of newly built homes, not for repeat buyers purchasing resale property, under the same December 2024 reforms. Stretching the amortization from 25 to 30 years lowers the monthly payment and can meaningfully raise what a stress-tested budget supports, which matters for a young household exactly like the one in this example.
Putting the whole calculation together
Line up everything above and the full sequence looks like this for our example couple. Gross income sets the ceiling through the GDS and TDS ratios. Existing debt (none, in their case) determines whether GDS or TDS ends up binding. The stress test then converts that monthly payment ceiling into a maximum mortgage amount using a rate two points above whatever they’re actually offered. Their down payment gets added on top of that mortgage figure to arrive at a final purchase price ceiling. Every one of those four steps can move the final number by tens of thousands of dollars, which is exactly why a rough income-based guess and an actual lender calculation rarely match.
A household with a car payment eating into their TDS room, or a lower down payment pushing them into a higher CMHC premium tier, would land somewhere different even with the identical $95,000 income. That’s the honest answer to “how much house can I afford.” It depends on four separate numbers working together, not one.
The costs people forget to factor in
Property tax and heat are already baked into the GDS calculation, but they’re often guessed rather than confirmed, and a low guess inflates your apparent affordability. Ask for the actual property tax bill on any home you’re seriously considering rather than estimating from the purchase price, since rates vary meaningfully by municipality and assessment. Condo fees deserve the same scrutiny, since only half counts toward GDS but the full amount still leaves your bank account every month.
Then there are the costs that never show up in a GDS or TDS calculation at all. Land transfer tax, legal fees, a home inspection, and (if you’re putting down less than 20 percent) the CMHC insurance premium itself, which gets added to your mortgage balance rather than paid upfront but still increases what you owe and what interest accrues on. Budgeting only to the edge of what a lender will approve leaves nothing for these closing costs or for the ordinary financial surprises that come with owning a home instead of renting one.
What else moves your number
Your credit score affects more than approval odds. A stronger score can unlock a better rate, and a better rate directly raises what your GDS ceiling will support, since less of every payment goes toward interest. The choice between a fixed and variable rate matters here too, since they can carry different contract rates at signing, which changes your stress-tested qualifying rate even though the 5.25 percent floor stays the same either way. If you’re weighing that decision, it’s worth understanding how variable rates actually behave before assuming the lower headline number automatically means more buying power.
Paying down existing debt before you apply is one of the few affordability levers fully within your control. Clearing a car loan or a credit card balance frees up TDS room directly, sometimes by more than a strong down payment would. And the Bank of Canada’s rate path matters more than most buyers realize, since a lower contract rate at signing lowers your stress-tested qualifying rate right along with it, stretching your affordability without you saving another dollar.
Running your own numbers
Start with your actual gross income and your actual current debts, not rounded estimates, then check both the 39 percent and 44 percent ceilings against them the way a lender would. Get a real property tax figure and a real heating cost estimate for the type of home you’re considering rather than guessing low. Run a mortgage calculator using a rate two points above what you’re currently being quoted, since that’s the number that will actually determine your approval, not the rate on the lender’s advertisement. Compare what that produces against current mortgage rates and CMHC’s own explanation of how insured mortgages work, check it against where fixed rates sit right now if you’re leaning that direction, and if the number still feels uncertain, a mortgage broker can run a real pre-approval against your actual financial picture before you start touring homes you might not qualify for.
