How Debt-Service Ratios Affect Mortgage Approval in Canada

Key Takeaway

Canadian lenders use two debt-service ratios to determine mortgage eligibility: the Gross Debt Service (GDS) ratio measures housing costs against income, while the Total Debt Service (TDS) ratio includes all debt payments. Most lenders require a GDS below 39 per cent and a TDS below 44 per cent, though stricter limits may apply under the OSFI mortgage stress test. Lowering your debt and increasing stable income improves both ratios and your approval chances.

Introduction

When you apply for a mortgage in Canada, lenders evaluate your ability to carry the debt using two critical calculations: the Gross Debt Service (GDS) ratio and the Total Debt Service (TDS) ratio. These percentages compare your housing costs and total debt obligations to your gross income, helping lenders assess whether you can afford the mortgage payments alongside your other financial commitments. Understanding how these ratios work and what limits apply is essential for anyone seeking mortgage approval, renewal, or refinancing.

What You Will Learn

This guide explains the GDS and TDS ratios, how Canadian lenders calculate them, the maximum thresholds you must meet, and practical steps to improve your ratios before applying for a mortgage.

Step 1: Understand the Gross Debt Service (GDS) Ratio

The GDS ratio measures your monthly housing costs as a percentage of your gross monthly income. Housing costs include your mortgage principal and interest payment, property taxes, heating costs, and (when applicable) 50 per cent of condominium fees.

The formula is:

GDS = (Mortgage Payment + Property Taxes + Heating + 50% Condo Fees) / Gross Monthly Income

Most Canadian lenders set a maximum GDS of 39 per cent. This means your housing expenses should not exceed 39 per cent of your gross income before taxes. The GDS focuses exclusively on housing, isolating the cost of owning your home from your other debt obligations.

According to the Financial Consumer Agency of Canada, the GDS ratio is one of the primary affordability measures lenders use to ensure borrowers are not over-extended on housing costs alone (FCAC, 2026).

Step 2: Understand the Total Debt Service (TDS) Ratio

The TDS ratio adds all your other debt payments to your housing costs and compares the total to your gross monthly income. This broader measure includes credit card minimum payments, car loans, lines of credit, student loans, and any other recurring debt obligations.

The formula is:

TDS = (GDS Housing Costs + All Other Debt Payments) / Gross Monthly Income

The standard maximum TDS for most lenders is 44 per cent, though some allow up to 42 per cent depending on the borrower profile and property type. The TDS reveals your overall debt load and whether you have enough income left after all obligations to manage a mortgage comfortably.

As outlined in foundational finance texts such as Principles of Finance, lenders use debt-to-income ratios to gauge creditworthiness and default risk, a principle applied directly in Canadian mortgage underwriting.

Step 3: Factor in the OSFI Mortgage Stress Test

Canadian federally regulated lenders must qualify you at a higher interest rate under the OSFI B-20 guideline, known as the mortgage stress test. You must meet the GDS and TDS limits using the greater of the Bank of Canada five-year benchmark rate or your contract rate plus two percentage points.

This means even if your actual mortgage rate is 4.5 per cent, the lender calculates your ratios using a qualifying rate of 6.5 per cent or higher. The stress test ensures you can still afford payments if rates rise when you renew your mortgage term. According to OSFI, this measure protects borrowers from over-leveraging and reduces systemic risk in the housing market (OSFI, 2026).

Step 4: Calculate Your Own Ratios

Before applying, calculate your GDS and TDS to see where you stand. Add up your expected monthly mortgage payment (use a mortgage calculator with the stress-test rate), property taxes, heating estimate, and any condo fees. Divide by your gross monthly income for GDS. Then add all other monthly debt payments and divide again for TDS.

If either ratio exceeds the lender limits, you will need to reduce debt, increase income, or lower the purchase price and mortgage amount.

Step 5: Improve Your Ratios

To strengthen your mortgage application, take these steps:

Pay down high-interest debt such as credit cards and personal loans to reduce your TDS.
Increase your down payment to lower the mortgage amount and monthly payment, improving both GDS and TDS.
Add a co-applicant with stable income to increase total household income and lower the ratios.
Delay large purchases or new credit accounts until after your mortgage closes.
Provide documentation of stable, verifiable income (employment letters, tax returns, pay stubs) to maximize the income lenders count toward the ratio calculation.

Canada Mortgage and Housing Corporation recommends keeping housing costs well below the maximum thresholds to leave room for unexpected expenses and financial flexibility (CMHC, 2026).

Common Mistakes to Avoid

Do not assume you qualify for the maximum mortgage amount the calculator suggests. The stress test and ratio limits often reduce your actual borrowing power. Avoid taking on new debt close to your mortgage application, as every new payment raises your TDS. Do not underestimate property taxes or heating costs when calculating GDS, since lenders verify these figures and adjust your qualification accordingly.

Frequently Asked Questions

What if my ratios are over the limit?

You will not qualify for the mortgage amount you applied for. Reduce your purchase price, increase your down payment, pay down existing debt, or add a co-borrower to bring the ratios within acceptable ranges.

Do all lenders use the same GDS and TDS limits?

Federally regulated lenders follow OSFI guidelines with standard limits of 39 per cent GDS and 44 per cent TDS. Credit unions and private lenders may have slightly different thresholds, but most align closely with these benchmarks.

Can I exclude certain debts from the TDS calculation?

No. Lenders include all recurring debt obligations visible on your credit report and any liabilities you declare. The only exception is debt that will be paid off before your mortgage closes, confirmed with documentation.

Conclusion

The GDS and TDS ratios are the foundation of mortgage qualification in Canada. By keeping your housing costs below 39 per cent of gross income and your total debt load below 44 per cent, and by meeting the stress-test requirements, you maximize your chances of approval. Review your finances carefully, reduce unnecessary debt, and confirm your income documentation is current before you apply. For your specific situation, consult a licensed mortgage broker or your financial institution to verify the exact ratios and qualifying rate that apply to your mortgage application.

Financial Disclaimer: This article provides general educational information only and is not personalized financial, lending, legal, or tax advice, nor an offer or commitment to lend. Mortgage qualification criteria, debt-service ratio limits, and stress-test rules vary by lender, province, and individual circumstances. Interest rates and the Bank of Canada benchmark rate change frequently. Verify current limits, qualifying rates, and your personal eligibility with a licensed mortgage professional or your financial institution before making any decisions.