How Many Calories Do You Need? The Harris Benedict Equation

The Harris Benedict equation was formulated in 1919 and derived using 239 normal, healthy people spanning a wide age range. There was follow up work done in 1984 to improve the precision of the equation and it can estimate the energy expended (and therefore calories needed) in a normal, healthy person, to within around 10%.

This is highly accurate for a fairly simple formula and, with no medically-trained personnel needed, you can find out exactly how much you need to be eating to get the results that you need.

You can either go to the bottom of this post to calculate your calories automatically, or work through the detail directly below.

Here’s how:

Step 1

Calculate your Basal Metabolic Rate (BMR), the amount of calories that you need to continue to maintain your body weight if you’re not doing anything all day.

For Men:

BMR = 66.47 + ( 13.75 x weight in kg ) + ( 5.003 x height in cm ) – ( 6.755 x age in years )

For Women:

BMR = 655.1 + ( 9.563 x weight in kg ) + ( 1.850 x height in cm ) – ( 4.676 x age in years )

Step 2

Multiply the number that you get from above and multiply by the exercise level below. If you’re doing Insanity then you need to use the ‘moderately active’ or ‘very active’ multiplier.



Exercise Factor (multiply by)

Sedentary Little or no exercise 1.2
Lightly Active Light exercise (1 to 3 days per week) 1.375
Moderately Active Moderate exercise (3 to 5 days per week) 1.55
Very Active Hard exercise (6 to 7 days per week) 1.7
Extremely Active Hard daily exercise and/or a physical job 1.9

Step 3

Now you have your number for weight maintenance. You’ll need to adjust this number up or down, depending on whether you want to gain or lose weight. Just remove or add the number of calories outlined below.

This gives you your daily calorie requirement!


Calorie Adjustment

Lose Weight Remove 500 calories
Maintain Weight Do nothing, use the formula from step 2
Gain Weight Add 250 to 300 calories

The Harris Benedict Calculator

Use the quick calculator below, but remember to add your gain, lose or maintain calories from step 3.

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