Several factors contribute to a person's basal metabolic rate (BMR), which indicates the number of calories burned at rest. Key contributors include age, sex, body size, and composition. Generally, younger individuals tend to have a higher BMR due to increased muscle mass, which burns more calories than fat. Hormones, such as thyroid hormones, also significantly affect metabolism. Additionally, genetic factors play a role, influencing how efficiently the body converts food into energy. Understanding BMR can aid in developing appropriate diet and exercise plans for weight management.