The two most common mortgages are the fixed rate mortgage and the adjustable rate mortgage (ARM). With a fixed rate mortgage, the interest rate remains the same over the life of the loan. With an ARM, the rate can change at a predetermined interval, such as once every five years. The rate for an ARM is tied to changes in a published index such as US Treasury bonds. If the index goes up or down, the mortgage rate and payment does the same. Most ARMs have maximum and minimum rates referred to as a ceiling and a floor rate.