Interest payments during the early years of your ARM loan will be generally lower than those of a fixed rate mortgage.
Your initial interest rate will remain the same for a period of 5, 7 or 10 years, depending on the mortgage you choose, and then adjust annually, based upon current interest rates.
There's a limit to how high your monthly interest payment may go when your ARM loan rate adjusts, and over the life of the loan. Or you can refinance into a fixed rate mortgage if you prefer to lock in a rate.