Mortgage Affordability Calculator
The question every buyer asks: what's the most expensive home I actually qualify for? This works it out the way a Canadian lender does — GDS and TDS ratios, the stress test, and your down payment's own ceiling.
How rates move your budget
Maximum purchase price at contract rates from 3% to 7% — everything else held constant. The stress test amplifies every move.
Price by down payment
What you could buy at different down-payment percentages of the resulting price. More down means less CMHC, and past 20% no insurance at all.
| Down % | Down $ | Max price | Mortgage | CMHC | Payment/mo |
|---|
How this is calculated
The two ratios lenders use
Every Canadian lender runs your numbers through two debt-service tests and takes the lower result:
GDS (Gross Debt Service) — max 39%. Housing costs only: GDS budget = income ÷ 12 × 0.39. Housing = mortgage payment + property tax + heat + ½ of condo fees.
TDS (Total Debt Service) — max 44%. Housing plus every other debt payment: TDS budget = income ÷ 12 × 0.44 − monthly debts.
Your money available for principal & interest is min(GDS, TDS) − tax ÷ 12 − heat − 0.5 × condo. Whichever ratio produces the smaller housing budget is the one that binds — the calculator names it in the verdict box.
The stress test (why qualifying ≠ contract)
OSFI B-20 requires lenders to test you at the qualifying rate — the greater of your contract rate + 2% or 5.25%. The maximum mortgage is solved from the qualifying payment, so the mortgage you can borrow is smaller than a naïve calculator at your contract rate would suggest. The monthly payment shown in the metrics is then re-computed on that mortgage at your real contract rate, which is why it's lower than the qualifying payment you were tested against.
Solving for the loan
Given the available payment pay, the maximum loan is the present value of that payment stream: L = pay × (1 − (1 + r)⁻ⁿ) ÷ r, where n is amortization in months and r = (1 + qualifying ÷ 2)^(2/12) − 1 — the effective monthly rate from Canada's semi-annual compounding.
CMHC and the down payment ceiling
Below 20% down, default insurance is mandatory and its premium (0.60%–4.00% of the loan, +0.20% for an insured 30-year amortization for first-time buyers and new builds) is added to the mortgage. Because the premium depends on the loan-to-value, which depends on the price, the calculator iterates a few times to a stable answer. Two hard ceilings can override your income: the minimum down payment (5% of the first $500,000, 10% above, 20% at $1.5M+) and the rule that insured mortgages are unavailable at $1.5M or more. When one of these caps your price below your income-based budget, the verdict box flags it.
What this doesn't model
Land transfer tax, closing costs, lender-specific overlays, self-employment income adjustments, or credit-score pricing. Property tax defaults to a flat $4,000 rather than a percentage of the (unknown) price. Pair this with the mortgage payment calculator, land transfer tax calculator, and rent vs. buy calculator for the full picture. Rules and tiers confirmed as of July 2026 (OSFI B-20, CMHC, FCAC).