When you choose a mortgage with an adjustable rate, you often benefit from a lower initial interest rate that lasts for a certain period of time. After that, the rate adjusts, either up or down, depending on market conditions. ARMs are helpful if you want lower monthly payments at the beginning or if you want to buy a house that's slightly out of your budget, but the payments aren't fixed. This calculator helps you figure out how the rate adjustments could impact your finances over time.