The Debt-to-Income Ratio is the ratio of gross monthly income (before taxes) to monthly debt payments. Debts can include car payments, mortgages, student loans and credit cards. The debt-to-income ratio is a key factor to qualify for a mortgage.

In mortgage underwriting, there are two debt-to-income ratios that are important. The front-end ratio is the ratio of the housing mortgage payment versus gross monthly income. The back-end ratio adds monthly housing payments to all other debts before dividing by gross monthly income.