Affordability Rule #1 Gross Debt Service (GDS)
The first rule is that your monthly housing costs should not be more than 32% of your gross monthly income. Housing costs include mortgages, taxes, and heating.
Affordability Rule #2 Total Debt Service (TDR)
The second rule is that your total combined monthly debt payments cannot be more than 40% of your gross monthly income. This includes credit card minimum payments, car payments, etc.