MetaboCalc uses the Harris-Benedict equation to give you an approximation

MetaboCalc uses the Harris-Benedict Equation to give you an approximation of how many calories you burn per day and at rest. It shows the base number, and also plus and Minus 5% and 20% due to errors inherent in that equation. Basically, this calculator is intended to show your RMR (Resting Metabolic Rate) or BMR (Basal Metabolic Rate). Actually, BMR and RMR are slightly different, but they`re often referred to as the same thing, so we`re not going to worry too much about that. It will also show your BMI (Body Mass Index) which is sometimes an indication of whether you are underweight, overweight, or just right for your height and weight. In general, if you consume the number of calories at the lower end of the scale, you should lose weight, but this is not always the case. MetaboCalc should be used as an approximation only. See your doctor before attempting any weight loss plan, as some of the lower ranges may lead to starvation! Every body is different, and there`s no easy way to determine a person`s metabolism just from an equation.