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A New Equation to Calculate the Calories Required to Lose Weight

March 26 2012

How do you use an equation to calculate the calories required to lose weight? It is always said that you need to burn 3500 calories to burn one found of fat. Hence the usual logic is to cut 500 calories per day and you will be losing 1 lb a week. This is called the 3500 calorie per pound rule.  

calculate calories required to lose weight

But this never happens in reality.

Why is the 3500C reduction to lose 1lb rule wrong?

Assumption: This calculation is based on the assumption that you are losing 87% of fat. But when people lose weight, they lose muscle mass too.

Metabolic Slow Down: As you lose weight, you also lose some muscle. This loss in muscle causes a decrease in resting metabolic rate.

Calories burned: As you lose weight, your body burns less calories to do the same amount of activity.

Starting Composition: It is now known that people with greater initial body fat levels lose less muscle compared to people with lower initial body fat levels.

How is the new equation different from the old equation?

Old equation: For a 224lb guy, a 500 calorie deficit/week will result in 50lb weight loss in the first year.

New equation: Based on the new model, for a 224lb guy, the body weight will plateau after losing 56 lbs in 10 years. Out of the 56 lbs, you will lose 22lb in the first year and the 95% of the this 56lb in 3 years.

The old equation predicts greater than 100% weight loss than the new equation!

What is this new dynamic equation?

These complex equations to calculate the calories required to lose weight have been integrated into a web-based program.

  • Enter your current weight, height, age and activity level
  • Enter your desired weight & duration you need to lose this weight
  • Enter the increase in physical activity
  • You will get the calories you should eat to reach this weight and the calories required to maintain this weight.
  • There are a lot more features in the results, like body fatness, results in tabular form and so forth.

new equation to calculate calorie to lose weight

For example, I am 165lb and 68in tall. In the top-middle panel, I have my goal weight (140lb) and desired time interval to achieve the goal (150 days).Running the simulation shows the required changes of calorie intake to meet the goal and then maintain the weight change. The simulated bodyweight trajectory is graphically displayed in the lower panel. Users can also modify the physical activity tosee how combinations of diet and exercise  can achieve the same goal.

Click the lick to open the body weight simulator: The New Equation


  • There is a 5% error in calculating the basal energy requirements
  • The adherence is assumed to be perfect
  • Changes in energy intake which can effect changes in energy expenditure. For example, people eating more after they work out
  • There are genetic factors which can change the weight lost or gained.

Practical Application

  • The old equation is static and clearly overestimates the predicted weight loss
  • The new equation takes into account the loss in muscle mass and the drop in calorie expenditure with weight loss
  • Though it has limitations, the  new equation can predict the calories required or activity needed  to lose a certain amount of weight in a certain duration with a greater accuracy than it has ever been possible.

Reference 1

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