An adjustable rate mortgage is a mortgage loan that is fixed for a set period of time and then adjusts based on the rates during the adjustment period. Some common adjustable rate mortgage loans terms are 1/1, 3/1, 5/1, 7/1, and 10/1. The first number in what appears to be a fraction is the amount of time the rate stays fixed. The second number is the amount of time between adjustments. For example a 5/1 Adjustable rate mortgage would stay fixed for 5 years and then adjust annually.

An adjustable rate mortgage generally offers a lower rate than a fixed rate loan initially; however, it could adjust to a higher rate than the initial fixed rate mortgage would have been. An Adjustable rate mortgage, also called an ARM, is very good for a person that knows specifically how long they will be living at a specific residence. In other words, a person who knows for a fact that they will be moving in four years would benefit from a 5/1 ARM because they would be moving out of that home and mortgage prior to the first adjustment period.

Adjustable rate mortgage loans also have an adjustment cap and a lifetime cap. For example a 5/1 arm could have an adjustment cap of 2% and a lifetime cap of 6%. So in a worst case scenario, a 5/1 Arm with a 2/9 cap and an initial rate of 5% would stay fixed at 5% for five years. At the five year mark the rate could adjust a maximum of 2% to 7%, after another year it could adjust 2% to 9% and after the next year could adjust to 11%. 11% would be the lifetime cap and therefore the adjustable rate mortgage could not increase any more. If the rates go down however, the rate could adjust lower after any given year.

There is however a floor rate which is the minimum rate the loan could ever achieve. In other words if the loan started at 5% and the floor rate was 4% the interest rate would never drop below 4%.

The difference between a fixed rate and adjustable rate mortgage is the fact that a fixed rate loan may start at 6.5% instead of 5% so for the first 5 years one would be receiving an interest rate 1.5% below that of a fixed.