Lenders don't decide what you can afford — they decide what you can qualify for. Understanding the ratios and stress tests that drive that number puts you in control.
What you'll learn
01
Five inputs shape how much mortgage a lender will approve.
Income
Gross household income — before tax — sets the ceiling on how much housing cost a lender will approve.
Monthly debts
Existing loan payments reduce the room available for a mortgage. Every dollar of debt lowers your qualifying range.
Down payment
A larger down payment shrinks the mortgage required — and can eliminate default insurance.
Mortgage rate
The contracted rate sets your actual payment. Even a half-point difference adds tens of thousands over the amortization.
Qualifying rate
Lenders test your ability to handle a higher rate than the one offered, protecting both sides from payment shock.
02
Ratios, stress tests, and the one rule that catches most buyers off guard.
Housing costs (mortgage, property tax, heat, 50% of condo fees) ÷ gross monthly income. A GDS around 32–39% is a commonly used guideline — thresholds vary by lender.
GDS — illustrative example
Contracted-rate calculation · property costs illustrative
Actual qualification uses the stress-test rate. Property tax and heat estimates vary by location.
GDS costs plus all other monthly debts (car, student, credit card minimums) ÷ gross monthly income. Around 44% is a commonly cited guideline — lenders assess holistically.
TDS — illustrative example
Contracted-rate calculation · CA$650/mo other debt
Close to the common guideline — typical for a household with moderate existing debt.
OSFI requires lenders to qualify borrowers at the higher of: contracted rate + 2%, or the Bank of Canada's minimum qualifying rate (MQR). At 5.19% contracted, you must qualify at 7.19%. Verify the current MQR before any application.
Housing costs only ÷ gross income. Often around 28–31% for conventional loans — lender guidelines vary.
All monthly debts ÷ gross income. Conventional loans may approve up to ~45–50% with compensating factors — thresholds vary by loan type and profile.
The US has no direct equivalent to Canada's OSFI B-20 rule. Individual lenders may apply their own rate buffers — ask each lender directly.
Quick comparison
Canada
United States
Ratios
GDS + TDS
Front-end + back-end DTI
Stress test
Mandatory (OSFI B-20)
No federal requirement
Compounding
Semi-annual
Monthly
03
One realistic Canadian household, with four levers you can pull to improve the outcome.
Sample inputs
Gross Income
CA$120,000 / yr
Monthly Debt
CA$650 / mo
Home Price
CA$650,000
Down Payment
CA$130,000 (20%)
Mortgage Rate
5.19%
Amortization
25 years
Estimated outputs
Mortgage required
CA$520,000
Qualifying rate
7.19%
Monthly payment
At contracted rate
CA$3,082
per month
Est. GDS ratio
~37%
Est. TDS ratio
~43%
Within range of typical guidelines
Illustrative only — actual result depends on lender, property costs, and current rules
Canadian semi-annual compounding (Interest Act). GDS/TDS at contracted rate with illustrative costs (CA$450/mo tax + CA$125/mo heat). Qualifying rate = max(5.19% + 2%, 5.25%) = 7.19%.
Higher income
A 25% income increase expands the housing-cost ceiling proportionally.
Lower monthly debt
Cutting debt reduces the TDS ratio by ~4–5 points, creating meaningful headroom.
Larger down payment
CA$35,000 more down reduces the mortgage to CA$485,000, saving ~CA$206/month.
Lower mortgage rate
A 0.69% rate reduction saves ~CA$204/month and lowers the stress-test rate too.
Payment figures use Canadian semi-annual compounding. Income and debt effects are directional — actual qualifying impact depends on lender thresholds.
04
Recognising them early is the difference between a smooth process and a late surprise.
Forgetting total ownership costs
Property tax, insurance, utilities, and condo fees commonly add CA$500–$1,500/month on top of the mortgage. Closing costs — legal fees, land transfer tax, and inspection — also run 1.5–4% of the purchase price, separate from your down payment.
Ignoring the stress test
In Canada, federally regulated lenders qualify you at a rate significantly above your contracted rate. Shopping based on the contracted rate alone often leads to an unexpected shortfall when the lender runs the actual calculation.
Treating the lender's maximum as a personal budget
Approval reflects what a lender will lend — not the amount that leaves you resilient. Many households that borrow at their approval ceiling find little room for savings, emergencies, or life changes.
05
After calculating, FinCalc Smart can surface AI-assisted insights about affordability pressure, opportunity signals, and possible next steps — based on your numbers.
Educational purposes only. All scenarios, ratios, and payment figures on this page are illustrative estimates and do not constitute a mortgage approval, lending commitment, or any form of financial, tax, legal, or mortgage advice. Lending rules, qualifying rates, GDS/TDS thresholds, and debt-ratio guidelines vary by lender, mortgage product, applicant profile, and province or state, and change over time. Always consult a licensed mortgage professional before making any borrowing or real-estate decision.