The Harris Benedict Equation 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 underestimate calorie needs) and the very fat (will overestimate calorie needs).
First, determine your BMR using our BMR Calculator or our BMR Formula.
Harris Benedict Formula 

To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:

Total Calorie Needs Example
If you are sedentary, multiply your BMR (1745) by 1.2 = 2094. This is the total number of calories you need in order to maintain your current weight.
Once you know the number of calories needed to maintain your weight, you can easily calculate the number of calories you need to eat in order to gain or lose weight:
 Calorie intake to gain weight
 Calorie intake to lose weight