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:
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.
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.
10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) + 5
10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) - 161.
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
21.6 * Fat Free Mass + 370
Where Fat Free Mass = Weight - (Body Fat Percentage * Weight).
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.
66.5 + (13.75 X weight in kg) + (5.003 X height in cm) - (6.775 X age in years)
655.1 + (9.563 X weight in kg) + (1.85 X height in cm) - (4.676 X age in years)
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.