Debt -to-Income Ratios and Car Payments You see, when determining your ability to qualify for a mortgage, a lender looks at what is called your "debt-to-income" ratio. A debt-to-income ratio is the percentage of your gross monthly income (before taxes) that you spend on debt. This will include your monthly housing costs, including principal, interest, taxes, insurance, and homeowner’s association fees, if any. It will also include your monthly consumer debt, including credit cards, student loans, installment debt, and…. …car payments