If you are unable to use our BMR Calculator, or if you are interested in how BMR is calculated, this page has the mathematical BMR Formulas.
The BMR formula uses the variables of height, weight, age and gender to calculate the Basal Metabolic Rate (BMR). This is more accurate than calculating calorie needs based on body weight alone. The only factor it omits is lean body mass and thus the ratio of muscle-to-fat a body has.
Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will underestimate calorie needs) and the very fat (will over-estimate calorie needs).
The formula listed below is the original Harris Benedict formula (1918). There have been many improvements over the years to this formula, all of which can be seen here.
English BMR Formula (Imperial)
Women: BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)
Men: BMR = 66 + (6.23 x weight in pounds) + (12.7 x height in inches) - (6.8 x age in years)
Metric BMR Formula
Women: BMR = 655 + (9.6 x weight in kg) + (1.8 x height in cm) - (4.7 x age in years)
Men: BMR = 66 + (13.7 x weight in kg) + (5 x height in cm) - (6.8 x age in years)
Once you know your BMR, you can calculate your daily calorie needs based on your physical activity level.