It’s the No. 1 reason that mortgage applicants nationwide get rejected: They’re carrying too much debt relative to their monthly incomes. It’s especially a deal-killer for millennials early in their careers who have to stretch every month to pay the rent and other bills. But here’s some good news: The country’s largest source of mortgage money, Fannie Mae, soon plans to ease its debt-to-income (DTI) requirements, potentially opening the door to home-purchase mortgages for large numbers of new buyers. Fannie will be raising its DTI ceiling from the current 45 percent to 50 percent as of July 29.