What GDS measures
Gross Debt Service divides qualifying monthly housing costs by gross monthly household income. Housing costs generally include the qualifying mortgage payment, property taxes, heating and 50% of condominium fees.
- GDS = monthly housing costs ÷ gross monthly income
- A $3,900 housing cost on $10,000 gross monthly income equals 39%
- Lower property costs can leave more room for the mortgage payment
What TDS adds
Total Debt Service uses the same housing costs and adds recurring debt obligations such as car loans, student loans and required credit-card payments. That is why two households with the same income and down payment can receive very different estimates.
- TDS = housing costs + other monthly debts, divided by gross monthly income
- A $500 car payment directly reduces room under the TDS limit
- Paying off debt may matter more than adding the same amount to a down payment
Why your lender's result may differ
The ratio is only one part of underwriting. Credit history, income stability, property type, loan insurance, documentation and lender-specific policies can change the result. Use the ratios to understand sensitivity, then obtain a formal assessment before making a firm commitment.
Worked example: calculate both ratios
Assume gross monthly household income of $10,000, qualifying housing costs of $3,500 and other required debt payments of $600. GDS is $3,500 ÷ $10,000 = 35%. TDS is ($3,500 + $600) ÷ $10,000 = 41%.
This example sits below the commonly published 39% GDS and 44% TDS reference maximums, but that does not guarantee approval. The lender still reviews the income source, credit, property, documentation and its own underwriting rules.
What to include in monthly debt
Use required payments, not optional extra payments. Include recurring obligations a lender will count, such as car and student-loan payments and the applicable required credit-card payment. Do not hide debts or assume a balance will disappear before closing unless it will actually be repaid and documented.
- Enter the required monthly debt payment in the calculator.
- Run a second scenario only if a debt will be fully repaid before qualification.
- Ask the lender how secured lines of credit, support payments or rental-property obligations will be treated.
Step-by-step
How to use the affordability calculator
- 1Convert gross annual household income to gross monthly income.
- 2Enter property tax, heating and 50% of condo fees with the qualifying mortgage payment for the GDS side.
- 3Add required monthly payments for loans, credit cards and other debts for the TDS side.
- 4Select Calculate estimate and test one change at a time, such as paying off a car loan or choosing a lower-cost property.
Frequently asked questions
Are 39% GDS and 44% TDS guaranteed approval limits?
No. They are commonly published CMHC maximum thresholds for the referenced insured program. A lender may apply different or lower limits.
Does a credit-card balance count in TDS?
The required monthly payment normally matters for the ratio. The calculator asks for the monthly debt obligation rather than the total balance.
Why can TDS be the binding ratio?
TDS includes the housing costs used in GDS plus other required debt payments. Car, student-loan and credit-card payments can therefore reduce mortgage room.
Try your own numbers
Canada House Affordability Calculator
Enter income, debts, down payment, interest rate and property costs, then select Calculate estimate to reveal the result and breakdown.
Related Canadian home-buying guides
Official sources
- CMHC Home Start: maximum GDS and TDS thresholds
- Financial Consumer Agency of Canada: mortgage affordability
Sources reviewed October 6, 2026. Rules and lender policies can change.