To calculate your DTI ratio, you'll need to add up all of your monthly payments that are related to debt (such as credit cards, mortgages, student loans, etc.) This free debt-to-income ratio calculator.Simply use your budget to fill in the numbers below and click "CALCULATE" to determine your personal DTI. Lenders factor in all your monthly debt payments when calculating your DTI ratio. FHA lenders consider two different ratios before issuing a loan. When calculating the percentage of gross monthly income that goes toward paying off debt, you get your DTI ratio. Your DTI is calculated using your total monthly obligations and dividing them into your total monthly gross income. Debttoincome ratio (DTI) is the relationship between your monthly debt payments and your monthly gross income. FHA lenders consider two different ratios before issuing a loan. Express the resulting ratio as a percentage.