Background Image - Math of WL

Are you setting fat loss targets for yourself and failing to achieve them? Well your targets might not be all that realistic. Fortunately, there is a method you can use to make a good approximation of how fast you can lose fat.

Understanding the mathematics behind fat loss can help you set realistic goals given your current diet and exercise levels. It can also help you modify your exercise and diet in a way that is in line with your fitness goals.

While taking you through the process of calculating it, I will take the example of one of our happy users, Alia (name changed). You can do the same calculations for yourself by following the steps below. If you want to stay away from all the formulas, you can download our Beginner’s DIY Planner which has all the formulas built in. You can just input your numbers there and see the result.

Our friend Alia currently weighs 82kgs, is 5ft 6in tall and is currently 30 years old. She wants to create a sustainable fat loss plan for herself. However, since she has a job that keeps her busy through the day, she cannot invest a lot of time and effort in this. She is following an approach of moderate exercise and cutting down on some unhealthy diet habits.

Step 1: Calculate your resting metabolism (BMR)

The first step for her is to calculate her resting metabolism. Resting metabolism is the number of calories required for the basic functioning of your body. It is number of calories you will burn even if you perform absolutely no physical activity through the day – just spend the entire day lying on your bed.

To calculate this we use the best equation currently available (Mifflin St. Jeor equation)

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

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

Based on her age, gender, height and weight, we estimated that Alia’s resting metabolism is 1570kcal.

Step 2: Calculate average daily calorie burn

Now we need to calculate the total number of calories she burns in a day. For that we need to know how physically active she is during the day and how often she exercises. Based on activity levels, a multiplier is calculated which when multiplied to the BMR gives you an estimate of the average number of calories you burn in a day.

The figures below will give you an estimate of what your multiplier should be.

Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extr. active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.)

Alia has a lightly active job and she exercises 5-6 times a week for about 30 minutes. Based on this information we estimate that she has a multiplier value of 1.6 and she burns approximately 2,500 kcal everyday.

Step 3: Estimate the calories in your daily diet

The next step is to estimate the number of calories you consume every day. For this, refer to any online calorie calculator or the calculator we have provided in the excel file with specific emphasis on Indian foods.

Alia plans her diet and notes down all the food items she eats on an average day to calculate how many calories she consumes every day. She realizes that her average diet has 2000 kcal, giving her a calorie deficit of 500 calories every day. This is within the maximum 20% deficit recommended for sustainable weight loss.

Step 4: Calculate daily deficit and no. of days it will take to burn 1 kg of fat

Now, it takes about 7700 kcal to burn 1 kg of body fat. She has a calorie deficit of 500 calories every day. So it will take her (7700/500 = 15 days) to burn 1 kg of fat. This is exactly the goal she has set. She wants to lose 2 kgs per month.

You can play around with your calorie deficits and exercise programme to see how the days required to burn 1 kg of fat changes.

Disclaimer – Please note that these are approximate calculations meant to give you an estimate of how long it takes to lose weight. Many things can change causing the number to be different. For instance, Indian foods contain a variety of ingredients and the ratios in which the ingredients are used can change your calculations.