The typical 30-year fixed jumbo mortgage rate fell 4 basis points to 4.15 percent. The average 5/1 adjustable mortgage rate increased 1 basis point to 3.46 percent. A basis point is one-hundredth of 1 percent. For the purposes of Bankrate's survey, a jumbo mortgage is a loan that is at least $650,000. With a 5/1 ARM, the rate is fixed for five years and adjusted annually thereafter.