The average rate for a 30-year fixed-rate mortgage dropped .07 percentage points for the week ending Sept. 10, reaching 2.86 percent — anew low since Freddie Mac began conducting the survey in 1971. This time last year, the mortgage rates averaged 3.56 percent. Fifteen-year mortgages declined, too, to an average of 2.37, while five-year mortgages were up 18 percentage points to 3.11.