As a personal trainer, I’m often asked how many calories my clients should be eating every day to lose fat. To do this, we must first work out how many calories an individual requires to maintain their current weight. The Harris Bendict Formula, is the most accurate to date in my opinion.
Harris Benedict Formula
This is a calorie formula using the factors of height, weight, age, and sex to determine basal metabolic rate (BMR). This makes it more accurate than determining calorie needs based on total bodyweight alone. The only variable it does not take into consideration is the amount of lean body mass (muscle). Therefore, it will be very accurate in all but the extremely muscular (it will underestimate caloric needs) and the extremely over fat (it will overestimate caloric needs).
Men: BMR = 66 + (13.7 * weight in kg) + (5 * height in cm) – (6.8 * age)
Women: BMR = 655 + (9.6 * weight in kg) + (1.8 * height in cm) – (4.7 * age)
Note: 1 inch = 2.54 cm
1 kg = 2.2 lbs
1 stone = 14 lbs
For example, Tom is 41 years old, he’s 6’2” tall and weighs 14 stone and 6 lbs. Tom works as a painter and decorator but doesn’t go to the gym (we’ll see why his occupation and exercise regime is relevant soon).
Tom’s BMR = 655 + (13.7 * 91.6kg) + (5 * 188cm) – (6.8 * 41) = 2571
Now that we know Tom’s BMR, we can calculate Total Daily Energy Expenditure (TDEE) by multiplying the BMR by the activity multiplier below:
Sedentary BMR * 1.2 (little or no exercise, desk job)
Light active BMR * 1.375 (light exercise/sports 1-3 days/week)
Mod. active BMR * 1.55 (moderate exercise/sports 3-5 days/week)
Very active BMR * 1.725 (hard exercise/sports 6-7 days/week)
Extra active BMR * 1.9 (hard daily exercise/sports physical job)
As Tom works as a painter and decorator but isn’t a gym goer, I’m going to decide he’ll go into the moderate active group (activity factor 1.55).
Tom’s TDEE = BMR * Activity Multiplier
2571 * 1.55 = 3985 calories/day
Another example, this time using a woman:
Jane is 27 years old, she’s 5’5” tall and weighs 8 stone and 8 lbs. Jane works as a sectary and goes to the gym 3 times a week.
Jane’s BMR = 655 + (9.6 * 54.4kg) + (1.8 * 165 cm) – (4.7 * 27) = 1347
I’m going to decide that Jane’s goes into the light active group (activity factor 1.375)
Jane’s TDEE = BMR * Activity Multiplier
1347 * 1.375 = 1852 calories/day