The traditional 30-year fixed-rate mortgage has a constant interest rate and monthly principal and interest payments that never change. It is the most popular mortgage type, so it can be a good choice if you plan to stay in your home for seven years or longer. If not, an adjustable-rate loan could be a cheaper option. When interest rates are low, though, a fixed-rate loan is generally not that much more expensive than an adjustable-rate mortgage, and may be a better deal in the long run because you can lock in the rate for the life of your loan.