Determining Daily Calorie Needs

Estimating daily calorie requirements is notoriously inaccurate. Even the very best calculators cannot determine the metabolic rate of an individual. Quite simply - everyone is different.

NOTE: The Free Dieting Calorie Calculator uses the following formulas to estimated daily energy requirements:

Uses Mifflin-St Jeor formula (see below).
Can also select old formula (Harris-Benedict), and a formula based on Lean Mass - but you must know your body fat percentage.
You can also choose BMR in the Exercise level. In this situation all weight loss calorie levels are blanked out.

The Best Guess

Calorie calculators will first estimate Basal Metabolic Rate (BMR). This is effectively the amount of energy expended per day. BMR is a measure of only the most basic functions (effectively the same as if you rested in bed the whole day). Other terms synonymous with BMR are Resting Metabolic Rate (RMR) and Resting Energy Expenditure (REE).

Once BMR has been estimated, various "activity" factors are applied. Once again these are best guesses. One individual may burn 100 calories on a 10 minute run - another individual may burn 150 calories.

Mifflin - St Jeor Formula

The Calorie Needs Calculator currently uses the formula proposed by MD Mifflin and ST St Jeor¹.

Why This Formula?
As recent as 2005, the ADA (American Dietetic Association) published a comparison of various equations². The Mifflin-St Jeor was found to be the most accurate.

Men
10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) + 5

Women
10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) - 161.

Lean Mass Formula

This can be selected on the calculator. It is a variation¹ on the basic Mifflin-St Jeor equation that will base the equation on Fat Free Mass (FFM) or Lean Mass. This is more accurate for those who are leaner (and who know their body fat percentage!).

Men & Women
19.7 * Fat Free Mass + 413

Where Fat Free Mass = Weight - (Body Fat Percentage * Weight).

Harris-Benedict Formula

This formula was created in 1919, and due to changing lifestyles, it tends to overstate calorie needs by 5%. The results tend to be skewed towards both obese and young people³.

Men
66.5 + (13.75 X weight in kg) + (5.003 X height in cm) - (6.775 X age in years)

Women
655.1 + (9.563 X weight in kg) + (1.85 X height in cm) - (4.676 X age in years)

The Freedieting Calculator

After calculating the BMR, exercise is factored in. Depending on the exercise level chosen, the BMR will be multiplied by anything from 1.2 to 1.9.

This provides us with maintenance calories. To get the fat loss figure - 20% is subtracted. The extreme fat loss figure has 40% subtracted BUT - there is a "rock bottom" figure that equates to 8 calories per pound of body weight - the extreme fat loss will never be less than this amount.

References

MD Mifflin, ST St Jeor, et al. A new predictive equation for resting energy expenditure in healthy individuals.
J Am Diet Assoc 2005:51:241-247. Link
Frankenfield DC, et al. Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review.
J Am Diet Assoc. 2005;105:775-789. Link
Frankenfield DC, et al. The Harris-Benedict studies of human basal metabolism: history and limitations.
J Am Diet Assoc. 1998;98:439-445.