If you use an American mortgage calculator for a Canadian mortgage, your payment will be slightly wrong. If you assume you can borrow based on the rate you were quoted, your budget will be substantially wrong. Both errors come from features specific to the Canadian system, and both are worth understanding before you start looking at properties.
Semi-annual compounding
Canadian fixed-rate mortgages are, by long-standing convention and the requirements of the Interest Act, quoted with interest compounded semi-annually, not in advance — even though you make payments monthly, biweekly or weekly. US mortgages generally compound monthly.
The practical effect is that you cannot simply divide the annual rate by 12 to get the monthly rate. You must first convert the semi-annual nominal rate into an effective monthly rate:
monthly rate = (1 + annual rate / 2) ^ (1/6) − 1
At 5%, dividing by 12 gives 0.41667% a month. The correct conversion gives approximately 0.41239%. The difference looks trivial and, on a single payment, is. Over a $600,000 mortgage amortised across 25 years it comes to a meaningful amount of money, and it is the reason a US-built calculator will quote you a payment a few dollars a month too high. Our Canadian mortgage calculator applies the semi-annual conversion.
A wrinkle: this convention applies to fixed-rate mortgages. Variable-rate mortgages in Canada are commonly compounded monthly. If you are comparing a fixed and a variable quote, you are not comparing identical mathematical objects, and the difference is small but real.
The stress test
Since 2018, borrowers at federally regulated lenders have had to demonstrate that they could still afford their mortgage at a rate higher than the one they are being offered. This is the minimum qualifying rate (MQR), set under OSFI's Guideline B-20.
The MQR has been the greater of:
- your contract rate plus 2 percentage points, or
- a fixed floor of 5.25%.
OSFI reviews this periodically and has adjusted both the framework and its scope over time — including changes to how it applies when borrowers switch lenders at renewal. Before you rely on a specific qualifying rate, confirm the current rule with OSFI or your lender; the mechanism is stable but the parameters are not permanent.
The consequence for your budget is significant. If you are offered 4.5%, you must qualify at 6.5%. Since your borrowing capacity scales roughly inversely with the rate you are tested at, testing at 6.5% instead of 4.5% cuts the mortgage you can qualify for by roughly 15 to 20%. On a household that could otherwise carry $600,000, that is around $100,000 of purchasing power removed.
Provincially regulated lenders such as credit unions are not bound by OSFI's guideline, though many apply a similar test voluntarily. Private lenders have their own criteria and, generally, considerably higher rates.
The debt service ratios
The stress test operates inside two ratio tests, which is where the actual limit is set:
- GDS (Gross Debt Service): housing costs — mortgage payment at the qualifying rate, property tax, heat, and half of any condo fees — as a share of gross income.
- TDS (Total Debt Service): all of the above plus every other debt payment — car loans, student loans, credit card minimums, lines of credit.
Common maximum thresholds are in the region of 39% for GDS and 44% for TDS, with insured mortgages typically held to the tighter end and some flexibility applied for strong applications. Lenders differ, so treat these as indicative rather than fixed.
The TDS ratio is the one that surprises people. A car payment of $600 a month does not reduce your borrowing capacity by $600 — it reduces it by roughly the mortgage that $600 a month would have serviced at the qualifying rate, which can be well over $80,000 of purchasing power. Clearing consumer debt before applying is often the single highest-leverage thing a buyer can do.
CMHC insurance
If your down payment is less than 20% of the purchase price, mortgage default insurance is mandatory. It protects the lender, not you, but you pay for it. It is provided by CMHC and two private insurers.
The premium is a percentage of the mortgage amount that rises as the down payment falls — from roughly 2.8% at a 5% down payment to around 2.8% to 4% depending on the tier and the loan-to-value band, with lower premiums at 10% and 15% down. Check the current premium schedule, as the bands are revised from time to time.
Key rules to know:
- The minimum down payment is 5% on the first $500,000 of purchase price, with a higher percentage required on the portion above that. Above a certain purchase price, insurance is not available at all and 20% down becomes mandatory. These thresholds have been adjusted in recent years — verify the current figures before planning around them.
- The premium is normally added to your mortgage rather than paid up front, so you pay interest on it for the life of the loan.
- Most provinces charge provincial sales tax on the premium, and that portion must be paid in cash at closing — it cannot be rolled into the mortgage. It is a genuine closing-cost surprise.
- Insured mortgages are capped at a 25-year amortisation in most cases, with a longer amortisation available for certain first-time buyer and new-build situations. A 30-year amortisation generally requires 20% down.
Putting it together
A realistic sequence before you shop:
- Work out your take-home pay, not your gross salary. That is what services a mortgage. Our take-home pay calculators will give you the annual figure.
- Clear or reduce consumer debt, because of its outsized effect on TDS.
- Calculate your payment at the qualifying rate, not the contract rate, to find what you can borrow.
- Then calculate your actual payment at the contract rate, so you know what you will really pay.
- Add the closing costs that are not the down payment: land transfer tax, legal fees, title insurance, inspection, and the PST on the CMHC premium if applicable.
- Budget for the renewal. Your rate is fixed for the term, not the amortisation — a five-year term on a 25-year amortisation means five renewals at unknown future rates.
That last point is what the stress test exists to address. It is frequently described as an obstacle, and for buyers at the margin it is. But it is testing something real: most Canadian mortgages renew several times over their life, and the rate you sign today is not the rate you will carry for twenty-five years.
Our mortgage calculator applies semi-annual compounding and includes CMHC insurance where the down payment is under 20%. If you are also assembling a down payment, our FHSA and Home Buyers' Plan guide covers the two registered accounts built for exactly that.
Frequently asked questions
What is the mortgage stress test in Canada?
Borrowers at federally regulated lenders must qualify at a minimum qualifying rate set under OSFI Guideline B-20 — historically the greater of the contract rate plus two percentage points or a 5.25% floor. You are approved based on that higher rate even though you pay the contract rate. Confirm the current rule with OSFI or your lender, as the parameters are reviewed periodically.
Why do Canadian mortgages compound semi-annually?
It is a long-standing Canadian convention reflected in the Interest Act's disclosure requirements for fixed-rate mortgages. It means you cannot simply divide the annual rate by twelve — the annual rate must be converted to an effective monthly rate, which produces a slightly lower payment than a US-style monthly-compounding calculation.
How much does the stress test reduce what I can borrow?
Qualifying at roughly two percentage points above your contract rate typically reduces borrowing capacity by around 15 to 20%, though the exact effect depends on your income, debts and the rates involved.
Do I have to pay CMHC insurance?
Mortgage default insurance is mandatory if your down payment is less than 20% of the purchase price. It protects the lender, not you, and the premium is usually added to the mortgage — though the provincial sales tax on the premium must be paid in cash at closing in most provinces.
Does the stress test apply to credit unions?
Not automatically. OSFI Guideline B-20 applies to federally regulated lenders. Provincially regulated lenders such as credit unions set their own policies, and many apply a comparable test voluntarily.
Sources
- OSFI — Guideline B-20, Residential Mortgage Underwriting Practices — Minimum qualifying rate and underwriting standards
- CMHC — Mortgage loan insurance cost — Premium schedule by loan-to-value band
- Financial Consumer Agency of Canada — Mortgages — Down payment minimums, debt service ratios, closing costs
- Interest Act (R.S.C., 1985, c. I-15), s. 6 — Statutory basis for semi-annual rate disclosure on mortgages
Written by the Calcova team and last checked against the sources above on 9 September 2026. This is general information about how the rules work, not personal tax or financial advice — see our disclaimer.
Related
Canadian mortgage calculator · FHSA and the Home Buyers' Plan · Debt payoff calculator · Ontario take-home pay