When you take out a RIO mortgage you will do so on a particular mortgage product. If choosing a fixed-rate product, you will pay at this rate for a set term which could be anything from 2 to 10 years depending on what is available. If choosing a variable rate this could go up or down. At the end of the deal, you can usually choose another product from your current lender or can remortgage to another lender. It’s possible that interest rates may have increased by then but it’s also possible that they may have decreased.