Basal metabolic rate calculator (Harris-Benedict)

The Harris-Benedict formula is the oldest widely used method for calculating basal metabolic rate. It was created in 1919 based on calorimetric measurements taken on a group of 239 people. The version for men reads: 66.47 + 13.75 × weight + 5 × height − 6.75 × age. For women: 655.1 + 9.563 × weight + 1.85 × height − 4.676 × age. For example, a man weighing 80 kg, 180 cm tall and 35 years old will get 66.47 + 1100 + 900 − 236.25 = 1830 kcal.

The resulting number is the energy the body needs at complete rest to sustain vital functions: heartbeat, breathing, temperature regulation and nervous system activity. Roughly one fifth goes to the brain's activity. To get the real daily energy requirement, the BMR must be multiplied by a physical activity factor, ranging from 1.2 for sedentary work to 1.9 for physical labor combined with daily training.

The formula does, however, have a clear flaw. The group studied a century ago came from people with a different average body composition than today's population, which causes the equation to give inflated values in people with overweight and obesity, in some studies by as much as 5–15 percent. That's why, since the nineties the Mifflin-St Jeor equation has been recommended more often. As with all equations of this type, Harris-Benedict knows nothing about muscle tissue content or hormonal status. Consider the figure an approximation with a margin of a dozen or so percent. In the case of hormonal disorders or before making a significant change to your diet, consult the result with a doctor.