How Debt-Service Ratios (GDS and TDS) Affect Mortgage Approval in Canada

Key Takeaway

Canadian lenders use two debt-service ratios to assess mortgage affordability: the Gross Debt Service (GDS) ratio, which measures housing costs alone, and the Total Debt Service (TDS) ratio, which includes all debt obligations. Most lenders require a GDS below 39 per cent and a TDS below 44 per cent, though these limits tighten under the OSFI mortgage stress test. Both ratios must fall within acceptable ranges to secure approval.

What Debt-Service Ratios Measure

Debt-service ratios quantify the portion of your gross monthly income consumed by debt obligations. According to the Financial Consumer Agency of Canada, lenders rely on these ratios to determine whether you can sustain mortgage payments alongside other financial commitments (FCAC, 2026).

The GDS ratio focuses exclusively on housing-related expenses: mortgage principal and interest, property taxes, heating costs, and 50 per cent of condominium fees if applicable. The TDS ratio expands the calculation to include all recurring debt payments such as credit cards, car loans, student loans, and lines of credit. As covered in Principles of Finance, debt-service coverage ratios have long served as fundamental measures of borrowing capacity in lending decisions.

Comparison Table: GDS vs TDS

Factor	GDS Ratio	TDS Ratio
What It Measures	Housing costs only	Housing costs plus all other debt
Components	Mortgage payment, property tax, heating, 50% condo fees	GDS components plus credit cards, loans, other debt
Typical Limit	39% of gross income	44% of gross income
Stress Test Impact	Calculated at qualifying rate (higher than contract rate)	Calculated at qualifying rate
Primary Use	Assess housing affordability alone	Assess overall debt load
Who It Constrains	Buyers with high property taxes or heating costs	Buyers carrying significant non-mortgage debt

How the GDS Ratio Works

The GDS ratio divides monthly housing costs by gross monthly income. For a household earning CAD 8,000 per month with a CAD 2,000 mortgage payment, CAD 400 property tax, and CAD 200 heating cost, the GDS is (2,000 + 400 + 200) / 8,000 = 32.5 per cent.

Most Canadian lenders cap the GDS at 39 per cent, meaning housing expenses cannot exceed roughly two-fifths of pre-tax income. This threshold applies to the qualifying payment calculated under the OSFI B-20 mortgage stress test, which requires approval at the higher of your contract rate plus two percentage points or the Bank of Canada’s five-year benchmark rate (OSFI, 2026). As of August 2026, the qualifying rate stands at 5.25 per cent, so even if you lock in a contract rate of 3.5 per cent, your GDS is tested at the higher qualifying rate.

When the GDS Ratio Matters Most

The GDS ratio constrains buyers in high property-tax regions or those purchasing properties with steep heating costs or condo fees. A detached home in a municipality with elevated tax rates may push the GDS above 39 per cent even when the mortgage principal is modest. Similarly, older homes with inefficient heating systems can inflate the ratio beyond lender limits.

How the TDS Ratio Works

The TDS ratio adds all non-housing debt obligations to the GDS numerator. Using the same household with a 32.5 per cent GDS, if monthly car loan payments total CAD 500 and minimum credit card payments are CAD 300, the TDS becomes (2,600 + 500 + 300) / 8,000 = 42.5 per cent.

Lenders typically require the TDS to remain below 44 per cent. The Canada Mortgage and Housing Corporation notes that exceeding this threshold signals elevated financial strain, reducing the likelihood of approval (CMHC, 2026).

When the TDS Ratio Matters Most

The TDS ratio becomes the binding constraint for applicants carrying substantial non-mortgage debt. High credit card balances, vehicle loans, or student debt can prevent qualification even when housing costs alone are reasonable. A buyer with a modest GDS of 30 per cent but CAD 1,500 in monthly non-housing debt might breach the 44 per cent TDS ceiling, forcing them to pay down existing obligations before applying.

How the Ratios Work Together

Lenders evaluate both ratios simultaneously. You must satisfy the GDS limit and the TDS limit to proceed. A low GDS does not excuse a high TDS, and vice versa.

In practice, the GDS ratio screens for housing affordability, while the TDS ratio screens for overall debt sustainability. Buyers with minimal non-housing debt may qualify for larger mortgages than those with identical incomes but heavy car loans or credit card balances.

Strategies to Improve Your Ratios

Reducing the GDS ratio requires lowering housing costs: a larger down payment cuts the mortgage principal and monthly payment, while selecting a property with lower taxes or heating expenses directly reduces the numerator. Choosing a longer amortization (up to 30 years with CMHC insurance on down payments below 20 per cent) also reduces monthly payments, though it increases total interest paid over the life of the loan.

Improving the TDS ratio demands paying down non-mortgage debt before applying. Clearing credit card balances, refinancing high-interest loans, or deferring large purchases until after mortgage approval can bring the TDS within acceptable bounds. Increasing gross income through additional employment or including a co-applicant’s income also raises the denominator, lowering both ratios.

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First-time buyers with minimal debt: Focus on keeping the GDS below 32 per cent to leave room for future expenses. Your TDS will naturally remain low if you avoid accumulating debt before purchasing.

Buyers with existing car loans or student debt: Prioritize paying down high-interest obligations before applying. Even small reductions in monthly debt payments can shift your TDS from 45 per cent to 43 per cent, moving you from rejection to approval.

High-income earners with strong credit: You may qualify at higher GDS and TDS thresholds with some lenders, but the stress test still applies. Confirm the qualifying rate calculation before assuming affordability.

Self-employed applicants: Lenders calculate income conservatively for self-employed borrowers, often using a two-year average of net income. This reduces the denominator in both ratios, requiring lower absolute debt levels to meet the percentage caps.

Conclusion

The GDS and TDS ratios serve as complementary filters in Canadian mortgage underwriting. The GDS ratio isolates housing affordability, while the TDS ratio captures total debt burden. Both are tested at the OSFI qualifying rate, not your contract rate, meaning you must demonstrate ability to service payments at a higher interest level than you will initially pay. Understanding these thresholds and adjusting your debt profile accordingly positions you to meet lender requirements and secure approval.

Verify current ratio limits and qualifying rates with a licensed mortgage broker, as lender policies and OSFI guidelines evolve. Mortgage qualification rules vary by lender, province, and your individual financial circumstances.

Financial Disclaimer: This article provides general educational information about Canadian mortgage debt-service ratios and is not personalized financial, lending, legal, or tax advice, nor an offer or commitment to lend. Debt-service ratio limits, qualifying rates, and lender policies vary by lender, province, and individual circumstances. Consult a licensed mortgage broker or financial institution for advice specific to your situation.