Fat Calc
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Body Weight PlannerWeight Goal Calculator

Calculate the amount of food energy you need to consume on a daily basis to reach your weight goal within your desired period of time and maintain it.

A change in body weight results from the difference between your food energy intake and the amount of energy expended by your body. Energy is expended in maintaining your body functions and in performing physical activities. For successful weight loss to occur, there must be an energy imbalance such that energy expenditure is greater than your energy intake.

There is a widespread myth that by reducing your energy intake by about 500 Calories (2 MJ) per day, you will slowly lose about 1 lb (0.5 kg) of weight a week. The National Institutes of Health and the American Dietetic Association have both erroneously stated this. This rule is sometimes referred to as the 3500 Calories per pound rule and is used in many weight loss calculators. It is overly simplistic and it's accuracy can be called into question especially in the long term. Unfortunately, it continues to be used in weight loss programs.

The rule's inaccuracy stems from the fact that it does not take into account the physiological changes that occur during weight loss. The amounts of body fat and lean tissue both change with an energy imbalance. Pound for pound, the energy content of body fat is about 5 times that of lean tissue. When you reduce your energy intake, muscle mass is lost along with fat mass. This reduces your resting metabolic rate, causing you to burn less energy.

The calculator incorporated into this app is based on a model developed by Kevin Hall, Ph. D., and a team of researchers at the National Institute of Health. It is a much more accurate model in determining energy expenditure and energy requirements for the purpose of weight management. It challenges the 3500 Calories per pound rule by taking into consideration the physiological changes that take place during weight loss. This includes changes in body fat, muscle mass, the thermic effects of feeding, glycogen and sodium.

Enter your body parameters, activity level, your weight goal and the period of time (start date to end date) in which you want to achieve your weight goal. If you don't know your activity level, click the Estimate button for an estimation.

Click Calculate to calculate the amount of food energy you need to consume on a daily basis to achieve your goal and maintain it.

Quantification of the effect of energy imbalance on bodyweight.
Lancet (2011 Aug 27) 27;378(9793):826-37.