Debt Service Ratio

What is debt service ratio in Canadian real estate?

A debt service ratio measures the percentage of a borrower's gross monthly income that goes toward debt obligations. Canadian lenders calculate two ratios for every mortgage application: Gross Debt Service (GDS) and Total Debt Service (TDS). Both must fall within lender-defined caps for the mortgage to be approved. The ratios are central to mortgage qualification under the federal stress test and OSFI's Guideline B-20.

Gross Debt Service (GDS) ratio

GDS measures housing-only costs as a percentage of gross income. The formula:

` GDS = (Mortgage payment + Property tax + Heat + 50% of condo fees) / Gross monthly income × 100 `

The four components are referred to as PITH + 50% of condo fees (Principal, Interest, Tax, Heat — and half of any condominium common-element fees if applicable). The 50% rule for condo fees is a federal underwriting standard reflecting that condo fees include both housing and reserve-fund contributions.

Standard GDS cap: 39% for insured mortgages (high-ratio, less than 20% down). For uninsured mortgages, lender policies vary but 35-39% is typical.

Total Debt Service (TDS) ratio

TDS adds all other debt obligations to the GDS components. The formula:

` TDS = (PITH + 50% of condo fees + Car loans + Credit card minimums + Lines of credit + Student loans + Other debts) / Gross monthly income × 100 `

The "other debts" line is where many applicants get tripped up. Lenders include the monthly minimum payment on revolving debt (credit cards, lines of credit) — typically 3% of the outstanding balance — even if the applicant intends to pay it off in full each month.

Standard TDS cap: 44% for insured mortgages. Uninsured mortgages: 42-44%.

Where this appears in your Humber program

Debt service ratios appear most heavily in Course 3: Additional Residential Properties in the financing module, and again in Course 4: Commercial Real Estate where commercial DCR (Debt Coverage Ratio) is the analog for income-producing properties. The exam tests both the formulas and the practical application to scenario problems.

A scenario the exam likes to test

A buyer earns $7,500 gross per month. They are buying a $600,000 condo with 20% down. Mortgage payment is $2,400. Property tax is $300/month. Heat estimate is $150. Condo fees are $400/month.

` GDS = ($2,400 + $300 + $150 + $200 [50% of condo fees]) / $7,500 = 41% `

41% exceeds the 39% insured-mortgage cap and is at the upper edge of uninsured policies. The exam typically asks what action a registrant should suggest: a larger down payment to reduce the mortgage amount, a longer amortization (raised back to 30 years for first-time buyers in 2024), or a less-expensive property.

Stress test implications

Since 2018, every uninsured mortgage in Canada must be qualified at the higher of: - The contracted interest rate plus 2%, OR - The Bank of Canada qualifying rate (currently 5.25% as a floor)

The stress-tested rate is the rate used in the GDS/TDS calculation, not the actual rate the borrower will pay. This is why a buyer who can "afford" a mortgage at 4.5% may still fail qualification at 6.5%. Real estate registrants should always reference the qualifying rate, not the contract rate, when discussing affordability with buyers.

GDS vs TDS

The exam frequently tests the distinction. The mnemonic: GDS is just housing; TDS is everything. A buyer with no other debts will have GDS = TDS. A buyer with a $400 car payment and $50/month minimum on a credit card adds $450 to TDS but not GDS.

Frequently asked questions

What is the maximum debt service ratio for an insured mortgage in Canada?

For insured (high-ratio) mortgages — those with less than 20% down payment — the federal maximums are 39% GDS and 44% TDS. Both ratios must fall under their caps for the mortgage to qualify. CMHC, Sagen, and Canada Guaranty all enforce these limits as part of their underwriting standards.

What counts as housing cost in the GDS calculation?

Housing costs in GDS are: monthly mortgage payment (principal + interest), monthly property tax, monthly heat costs, and 50% of monthly condo fees if the property is a condominium. The mnemonic PITH + 50% condo fees captures all four components.

Why does the lender include credit card minimums in TDS even if I pay in full?

Lenders use the stated monthly minimum payment (typically 3% of balance) regardless of the applicant's pay-in-full habits. The reasoning: if the applicant loses their job, the minimum is what the credit card issuer would actually require. This is conservative underwriting baked into Canadian residential mortgage standards under OSFI Guideline B-20.

How do debt service ratios interact with the mortgage stress test?

The stress test sets the interest rate used in the GDS/TDS calculation higher than the contract rate. The borrower must still meet the 39%/44% caps at the stress-tested rate. A common failure mode: the contracted rate gives a 38% GDS, but the stress-tested rate (contract + 2%) pushes it to 42% — disqualifying the application.

Practice this topic

ExamAce covers debt service ratios across Course 3 practice questions with calculation-style problems and stress-test scenarios that mirror the Humber exam format. For the broader finance picture, see the real estate finance pillar guide.