Interest rates are usually expressed as an annual percentage of the amount borrowed. You can choose a mortgage with an interest rate that is fixed for the entire term of the loan or one that changes throughout. A fixed-rate loan gives you the security of knowing that your interest rate will never change during the term of the loan. An adjustable-rate mortgage (called an ARM) has an interest rate that will vary during the life of the loan, with the possibility of both increases and decreases to the interest rate and consequently to your mortgage payments.