Debt to income (DTI) ratio is the percentage of your income that goes toward paying off your debt. These days, most lenders, especially mortgage and auto lenders make use of your debt to income ratio to determine how much debt you can handle. For instance, a mortgage lender will first take a look at your DTI ratio to figure out how much monthly mortgage amount you can handle after all your debts being paid. Yes, you can calculate on your own simply by using an online debt to income ratio calculator.