The Basal Metabolic Rate (BMR) of the body is the rate at which the body uses up energy at rest. This is the minimum amount of calories that a body requires to stay alive. This value varies from person to person, and even in the same individual, the BMR can differ at different periods of time, depending upon his or her age, health status, and external environment. Thus, while the BMR is known to reduce in hypothyroidism, the opposite occurs in hyperthyroidism. The BMR also increases at colder temperatures as the body burns more calories to stay warm.

Males have a greater muscle mass as compared to females, who have more body fat. Since muscles burn more calories in comparison to fat, a male usually has a BMR value that is higher than that of a female of the same age, with a similar build, and in the same environment.