Calculating your Caloric Needs

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 under-estimate calorie needs) and the very fat (will over-estimate calorie needs).

Metric BMR Formula
Women: BMR = 655 + ( 9.6 x weight in kilos ) + ( 1.8 x height in cm ) - ( 4.7 x age in years )

Men: BMR = 66 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) - ( 6.8 x age in years )

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

Sedentary (little or no exercise) : TDEE = BMR x 1.2
Lightly active (light exercise/sports 1-3 days/week) : TDEE = BMR x 1.375

Moderatetely active (moderate exercise/sports 3-5 days/week) : TDEE = BMR x 1.55
Very active (hard exercise/sports 6-7 days a week) : TDE = BMR x 1.725
Extra active (very hard exercise/sports & physical job or 2x training) : TDEE= BMR x 1.9

Alternate Method

Katch-McArdle formula (BMR based on lean body weight)If you have had your body composition tested and you know your lean body mass, then you can get the most accurate BMR estimate of all. This formula from Katch & McArdle takes into account lean mass and therefore is more accurate than a formula based on total body weight. The Harris Benedict equation has separate formulas for men and women because men generally have a higher LBM and this is factored into the men's formula. Since the Katch-McArdle formula accounts for LBM, this single formula applies equally to both men and women.

BMR (men and women) = 370 + (21.6 X lean mass in kg)

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

Sedentary (little or no exercise): TDEE = BMR x 1.2
Lightly active (light exercise/sports 1-3 days/week): = BMR x 1.375
Moderatetely active (moderate exercise/sports 3-5 days/week) TDEE = BMR x 1.55
Very active (hard exercise/sports 6-7 days a week): TDEE = BMR x 1.725
Extra active (very hard exercise/sports & physical job or 2x training): TDEE = BMR x 1.9

Calorie Needs to Lose Weight
There are approximately 3500 calories in a pound of stored body fat. So, if you create a 3500-calorie deficit through diet, exercise or a combination of both, you will lose one pound of body weight. (On average 75% of this is fat, 25% lean tissue). If you create a 7000 calorie deficit you will lose two pounds and so on. The calorie deficit can be achieved either by calorie-restriction alone, or by a combination of fewer calories in (diet) and more calories out (exercise). This combination of diet and exercise is best for lasting weight loss. Indeed, sustained weight loss is difficult or impossible without increased regular exercise.

If you want to lose fat, a useful guideline for lowering your calorie intake is to reduce your calories by at least 500, but not more than 1000 below your maintenance level. For people with only a small amount of weight to lose, 1000 calories will be too much of a deficit. As a guide to minimum calorie intake, the American College of Sports Medicine (ACSM) recommends that calorie levels never drop below 1200 calories per day for women or 1800 calories per day for men. Even these calorie levels are quite low.

An alternative way of calculating a safe minimum calorie-intake level is by reference to your body weight or current body weight. Reducing calories by 15-20% below your daily calorie maintenance needs is a useful start. You may increase this depending on your weight loss goals.

Source: http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/