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:

Activity Multiplier

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