Debt Ratio Calculator View Calculator Calculate your debt ratio or what percentage of your monthly income is used to pay fixed monthly costs. Enter your monthly income, monthly rent or mortgage expense, and other monthly expenses. This calculator will then show you what percentage of your monthly income goes to pay monthly debts and expenses. In general, most mortgage lenders do not want your total monthly housing expenses (including property taxes, private mortgage insurance (PMI), and association dues) to exceed 28% of your total gross monthly income. And your total debt ratio cannot exceed 36% of your total gross monthly income. Learn more about putting this calculator or other calculators on your website.