The interest rate you pay for a loan to buy real estate. The rate determines the cost of the loan and the amount of your monthly payment. Lenders set the rates, which can be fixed — that is, set at a given rate for the life of the loan — or variable, meaning they fluctuate according to a benchmark. Loans with variable rates are called adjustable-rate mortgages, or ARMs. Prevailing interest rates affect the mortgage rates set by lenders, and the buyer’s own credit history also comes into play. People with a poor credit score (known as subprime borrowers) are generally charged higher interest rates. Here’s where to find the best mortgage rates in your area.