Mortgage lenders use two calculations to help determine your eligibility for a mortgage - your Gross Debt Service (GDS) ratio and your Total Debt Service (TDS) ratio.

Your GDS ratio is the percentage of your gross monthly income used for mortgage payments, taxes and heating costs and - if you are buying a condominium - half of the monthly maintenance fees. As a general rule of thumb, your GDS ratio should not be more than 32% of your gross monthly income.

Your TDS ratio is the percentage of gross monthly income required to cover monthly housing costs, plus all your other debt payments, such as car loans or leases, credit card payments, lines of credit payments and any other debt. Generally, your TDS ratio should not be more than 40% of your gross monthly income.