An adjustable rate mortgage is a home loan that offers the opportunity for your mortgage rate to adjust after a certain number of years based on the market. The most popular ARM's are 5/1, 10/1 and 15/1. That means the rate will stay the same for 5, 10 or 15 years before adjusting to the market rate. These loans are best suited for those needing a very low rate and expect a significant increase in income later on.