Mortgage affordability is a key step in planning your home-buying budget. It estimates the largest mortgage you can responsibly take on based on your income, monthly debts and the costs of owning a property. Before you search listings or speak with a lender, use an online affordability calculator to get a realistic picture of what you can afford.
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What is mortgage affordability?
Mortgage affordability refers to the maximum mortgage amount a lender believes you can handle based on your gross household income, existing debt obligations and housing-related costs. The higher your affordability, the more you can borrow to purchase a home. Lenders typically review income, monthly housing costs (mortgage payments, property tax, heating, condo fees), and other debt payments such as credit cards and car loans. Your credit history and credit score will also influence the decision and the interest rate you qualify for.
Watch: What is mortgage affordability?
Why use a mortgage affordability calculator?
A mortgage affordability calculator quickly estimates how much you can borrow by combining your income, debts and anticipated homeownership costs. That estimate, together with your down payment, gives you a target maximum purchase price. Calculators are useful for testing scenarios—such as increasing income, paying down debt or saving a larger down payment—to see how those changes affect what you can afford.
These tools provide a starting point, but they use generalized rules. Always confirm affordability and specific mortgage terms with a lender or mortgage broker who can factor in the details of your financial profile, including credit score, employment history and unique circumstances that calculators don’t capture.
How does an affordability calculation work?
Before using a calculator, gather:
- Your gross annual income
- Any co-applicant’s income
- Monthly debt payments (credit cards, car loans, personal loans)
- Estimated monthly housing costs (mortgage principal and interest, property taxes, heating and condo fees)
Lenders use these figures to calculate two key ratios that guide mortgage approvals: the gross debt service (GDS) ratio and the total debt service (TDS) ratio.
Gross debt service (GDS) ratio
The GDS ratio compares monthly housing costs—mortgage principal and interest, property taxes, heating and condo fees—to your gross monthly income. For example, with $100,000 annual household income (about $8,333 per month), monthly housing costs of $3,000 represent a 36% GDS. Many mortgage insurers and lenders prefer a GDS no higher than around 39%.
Total debt service (TDS) ratio
The TDS ratio adds other monthly debt obligations—credit card minimums, car payments and other loan payments—to your housing costs, and divides the total by gross monthly income. Using the same $100,000 income example, $3,000 in housing costs plus $500 in other debts would equal a 42% TDS. Lenders often prefer a TDS at or below approximately 44%.
Mortgage affordability vs. maximum purchase price
Mortgage affordability estimates the loan amount you qualify for, while your maximum purchase price also depends on the down payment you can provide. For instance, if you qualify for a $475,000 mortgage and have $25,000 saved, your purchase limit is $500,000. If you increase your down payment to $50,000, your purchasing power rises without changing the mortgage amount. Remember to budget for closing costs, moving expenses and ongoing living costs when deciding on a final purchase price.
Make sure the monthly payment a lender will approve fits comfortably within your broader budget. Prepare a detailed household budget that includes groceries, utilities, transportation and discretionary spending so you can assess long-term affordability, not just the monthly mortgage payment.
How to increase mortgage affordability
If a calculator shows a lower affordability than you expected, consider these strategies:
- Increase household income: Higher gross income raises both the GDS and TDS thresholds, increasing the mortgage you can qualify for.
- Reduce debt: Paying down credit card balances or car loans lowers your monthly obligations and improves your TDS ratio.
- Add a co-signer: A co-signer with steady income can increase your approved mortgage amount, though they become legally responsible if you default.
- Save a larger down payment: Increasing your down payment boosts your maximum purchase price without increasing your mortgage principal. Tools like a first-home savings account or, for qualifying buyers, the Home Buyers’ Plan can help accelerate savings.
Ways to lower your monthly mortgage payment
If you want to lower monthly payments without reducing your mortgage amount, consider:
- Longer amortization: Extending the amortization period spreads payments over more years and cuts monthly commitments, but increases total interest paid over the mortgage term.
- Shop for a lower interest rate: Comparing lenders and working with a mortgage broker can help you find a more competitive rate, which directly reduces monthly payments.
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- CMHC mortgage insurance calculator
- Mortgage refinance calculator
- Mortgage renewal calculator
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