Here’s a quick way to calculate the maximum mortgage payment you may qualify for. First, take your monthly gross income and multiply it by 28%. Second, take you gross monthly income and multiply it by 48%. This first number is typically the maximum mortgage payment (including taxes, insurance and PMI if required) you would qualify for. The second number is the maximum amount of monthly debt you are allowed to have (includes installment loans, revolving debt, other mortgage payment, child support, etc.) Regardless of your credit, it’s always a good ideal to get pre-approved before you enter into a real estate transaction.