Basal metabolic rate (BMR) is the average daily amount of energy needed by a body when it is at rest. Heredity, height, body composition, and age determine a person's basal metabolic rate.

The energy in a person's basal metabolic rate is used to maintain body temperature and to power the heartbeat, breathing, and other organ functions. The average person's basal metabolic rate accounts for about two-thirds of the energy he or she expends.