The debt-to-income ratio is, simply, the way that mortgage lenders decide how much money you can comfortably afford to borrow. It is the percentage of your monthly gross income (before taxes) that is used to pay your monthly debts (not your monthly living expenses). Two calculations are involved, a front ratio and a back ratio, written in ratio form, i.e., 33/38.
The first number indicates the percentage of your monthly gross income used to pay housing costs, such as principal, interest, taxes, insurance, mortgage insurance and homeowners’ association dues. The second number indicates your monthly consumer debt, such as car payments, credit card debt, installment loans, etc. Other living expenses are not considered debt.