This calculator uses the Harris Benedict Equation, which is a formula that uses your BMR and then applies an activity factor to determine your total daily energy expenditure (calories). The only factor omitted by the Harris Benedict Equation is lean body mass. Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will under-estimate calorie needs) and the very fat (will over-estimate calorie needs).  The number generated by this calculator will serve as an estimated reference point of total daily caloric expenditure (Calories Out).  You may use the Calorie Counter to get an idea of caloric content (Calories In) of the foods you eat everyday.