Fixed rate mortgage loans maintain the same interest rate and monthly payment amount throughout the entire loan term. For adjustable rate mortgages, the rate and associated monthly payment may change over time. Fixed rates are set, or "locked", on a given day during the loan origination process, based on that day's rate, the lender's recommendation, and your choice, and that is the rate that determines the amount you will pay every month after the loan funds. Adjustable rates, on the other hand, are tied to an index and may change as that index fluctuates. With a fixed interest rate, you always know what you will be paying every month for your mortgage, even 10 years after funding. With an adjustable interest rate (also known as a "variable" rate), you may end up paying more or less per month as the rate goes up or down, although there is sometimes an introductory rate period where your rate is set for a certain length of time and then begins adjusting after a certain number of months or years.