A mortgage loan with payments usually lower than a fixed rate initially, but is subject to changes in interest rates. There are a variety of ARMs that can have an initial interest rate that lasts three to 10 years, adjusting annually thereafter. They are described as 3/1, 5/1, 7/1 and 10/1. A 3/1 ARM starts out with a low rate that lasts three years, then is adjusted annually. A 5/1 ARM has an introductory rate that lasts five years, and 7/1 and 10/1 ARMs have intro rates that last seven and 10 years. The monthly payment amount is usually subject to a cap.