Arm Mortgage Rates Today Variable Rate Definition 7 1 Adjustable Rate Mortgage Whats A 5/1 Arm All adjustable-rate mortgages have an overall cap. It would also help to be familiar with these terms in their numerical form, as this is the way in which your lender will illustrate the type of ARM you qualify for. 5/1: The five represents the amount of years the interest rate is fixed. The one indicates that the interest rate will adjust.You’ve found the perfect place and may have even started deciding where to put the furniture, but you still have one big obstacle standing in your way: getting a mortgage. buy a $250,000 home with.