The Mathematics of Weight Loss

This is a compilation of formulas, examples and MS Excel formulas on how to calculate calories for weight loss. By doing the maths for weight loss, it will assist in formulating a plan on how to approach weight loss and provide an understanding on the mechanics of it. It has also made me think of my food choices as well as exercises that I would consider sustainable during the decided duration of this weight loss plan. The calculations are done in metric (because that’s what I am used to). *Anyways, 1kg = 2.20462262 pounds

Step 1: Calculating Basal Metabolic Rate (BMR)

BMR basically means the calories or energy that would be required if you stayed in bed the entire day. Below is an example and as well as the Excel formula for calculating BMR based on the Mifflin St Jeor Equation which is supposed to be more accurate compared to the Harris-Benedict Equation (During the last 100 years, lifestyles have changed and Frankenfield et al. showed it to be about 5% more accurate). But if you’re in a rush, readily available BMR calculators are available online (e.g.


Step 2: Figuring out how much Weight to Lose (at least on paper)

Below is the worksheet of an example for figuring out how much weight will be lost based on a decided duration of 30 days and a commitment to brisk walk for 65 minutes everyday. Please refer to other details and assumptions laid out in the worksheet below.

Calculated Weight Loss


  1. The commonly used food ‘Calorie’  used in the calculation here is scientifically in actual fact ‘kilo calories’. Thus, 1 food ‘Calorie’ is actually 1 kilo calorie.
  2. 1 kg of body fats = 7,700 calories. Although 1 kg of pure fats equals to 9,000 calories, body fat is made up of about 90% fats, the rest of it is water and other cellular.
  3. It has been noted in numerous studies that we Humans tend to underestimate calorie intakes whilst overestimating calorie burned
  4. Here I will be using the Basal Metabolic Rate as the baseline for my caloric reductions. Why? Because I actually would like to succeed in losing weight. See point 3 above and the fact that I am quite sedentary (Meaning= I don’t move much).



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