Lenders generally use two standard formulae, what they call a "front ratio" and a "back ratio." The front ratio Also known as the housing-expense ratio, the front ratio suggests that your monthly house payment (including taxes and insurance) should not exceed 28% of your gross monthly income. The back ratio Also known as the debt-to-income ratio, the back ratio suggests that your total monthly home payment plus payments on other loans and credit cards should not exceed 36% of your gross monthly income.