The weekly average rate borrowers were quoted on Zillow Mortgage Marketplace for 30-year fixed mortgages decreased one basis point last week to 4.86 percent, down from 4.87 percent the week prior, according to the Zillow Mortgage Rate Monitor, compiled by leading real estate Web site Zillow.com®. Rates for 15-year fixed mortgages fell one basis point to 4.31 percent from 4.32 percent, and 5-1 adjustable rate mortgages fell one basis point to 3.79 percent, from 3.80 percent the week prior.