Fixed-rate mortgages are traditionally the most popular type of mortgage in America. They are typically taken out over a 30-year period, but lengths of 15 to 25 years are also available. The interest rate and monthly mortgage payment on a fixed-rate mortgage remain the same throughout the entire life of the loan. The main advantage of a fixed-rate mortgage is that the borrower knows exactly what their monthly costs will be until the entire mortgage has been completely paid out. The main disadvantage is that the borrower pays a premium for this guarantee in the form of slightly higher interest rates.