Michael Petruccelli says; Adjustable Rate Mortgages have fluctuating interest rates, but those fluctuations are usually limited to a certain amount. Those limitations may apply to how much the loan may adjust over a six month period, an annual period, and over the life of the loan, and are referred to as "caps." Some ARMs, although they may have a life cap, allow the interest rate to fluctuate freely, but require a certain minimum payment which can change once a year. There is a limit on how much that payment can change each year, and that limit is also referred to as a cap.
