DTI is a formula that compares certain debts you have to your gross income. DTI can be viewed as a 'front-end' or 'back-end' ratio. The front end ratio divides your gross income by the total of your mortgage payment, property taxes, and homeowner's insurance. The 'back-end' ratio additionally accounts for debts like car payments, credit card debts, and court-ordered child support or alimony obligations. DTI is expressed as a percentage, the percentage of your gross income that the debts utilize.