Mortgage Stress Test Math

A borrower can have one contract rate for the actual mortgage and a higher qualifying rate used only to test capacity. The qualifying payment—not necessarily the real payment—goes into GDS and TDS.

For current uninsured mortgages subject to OSFI's minimum qualifying rate, the test is the greater of the contractual mortgage rate plus 2 percentage points or 5.25%. Current CMHC and Sagen insured guidance cited here uses the same greater-of calculation for insured qualification.

Assume a $600,000 mortgage, 25-year amortization and 4.60% contract rate. Using Canadian semi-annual mortgage-rate conversion, the approximate monthly contract payment is $3,354.

The stress-test rate is 6.60% because 4.60% + 2.00% is greater than 5.25%. At 6.60%, the approximate qualifying payment becomes $4,055—about $701 more per month in the debt-service calculation even though the borrower does not actually pay that amount at closing.

Use the Mortgage Stress Test Calculator right here to compare the contract payment with the qualifying payment. If you are solving for buying power rather than one payment, use the Maximum Mortgage Calculator.

Above the 5.25% floor region, a higher contract rate generally pushes the qualifying rate higher as well. That means the mortgage payment can become more expensive in real life and the payment used for qualification can rise at the same time.

For a borrower already close to a GDS or TDS ceiling, that double effect can reduce maximum mortgage more than the headline rate change suggests. This is why HopeWell tests a rate range rather than treating one preapproval rate as permanent buying power.

Use the Mortgage Stress Test Calculator to change the rate in small steps, then use the Maximum Mortgage Calculator to see whether GDS or TDS becomes the binding constraint.

If the contract rate were 2.75%, adding two points produces 4.75%, so the 5.25% floor would govern. At a 4.00% contract rate, the plus-two rate is 6.00%, so the floor no longer matters.

The break-even contract rate is 3.25%: below that, the 5.25% floor is higher; above it, contract +2 is higher.

The stress test is mathematically important because it changes the mortgage principal-and-interest input in both GDS and TDS. Everything else can remain identical while the ratios worsen.

That is why a borrower can comfortably afford the real contractual payment and still fail lender qualification at the higher test payment.

When solving for maximum mortgage, the lender first determines how much qualifying housing payment fits the applicable GDS/TDS limits. It then converts that payment into a principal amount using the qualifying rate and amortization, not the lower contract rate.

The Maximum Mortgage Calculator follows that logic.

OSFI's current MQR guidance provides an exception for an eligible uninsured straight switch between federally regulated lenders where the mortgage amount and amortization are not increased. That does not turn every renewal, refinance or equity take-out into an exemption.

The distinction belongs in Mortgage Math because increasing the balance or amortization changes the transaction being tested.

A simple renewal with the existing lender is not a new mortgage qualification in the same way as a refinance. A straight switch may fall within OSFI's current exception if its conditions are met. A refinance that adds funds or extends amortization is different and generally requires full requalification under the applicable lender rules.

Use Renew vs Switch vs Refinance for the transaction-choice layer.

The qualifying rate is only one input. The lender still has to determine qualifying income, rental treatment and liabilities. A conventional ratio exception does not mean the lender can ignore the applicable MQR.

Likewise, changing the lender to obtain a better rental worksheet can improve TDS while the stress-test rate itself remains unchanged.

Use the Mortgage Stress Test Calculator to compare contract and qualifying payments, then feed the qualifying payment into GDS/TDS. Use Mortgage Interest Rates Explained if the distinction between contract and qualifying rates is unclear.