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How to Calculate Your Weight Loss

Young woman making calculations on her phone

Calculating your weight loss is a great way to find out how far you have come.

To calculate the percentage of weight lost, grab a calculator and follow these steps.

The quick and easy way

Your percent weight change is a very quick and easy snapshot of your weight loss as a whole. This quick math that will compare your pre-op weight to your current weight.

(Pre-op weight – Current weight) / (pre-op weight)  x 100 = % body weight change

Example: Your pre-op weight was 320 lbs, and your current weight is 200 lbs

(320-200) / (320) x 100 = 37% total body weight loss

The full picture

Calculating your weight loss based on your excess body weight – instead of your weight as a whole – is what is typically used in the bariatric clinic.

It requires a few extra calculations, but it gives us more precise information regarding where you are in your weight loss journey compared with your own healthy range.

There are a few steps, but don’t be intimidated, just follow along:

Step 1

In order to determine your excess body weight, you'll need to find the weight that would put you at a healthy Body Mass Index (BMI) of 25. A healthy BMI ranges from 18-24.9 (for the purpose of this calculation, we will round it to 25). 

25 x (height in inches x height in inches / 703) = Weight in lbs to be at a BMI of 25


Example:  You are 5’7” (67 inches; Remember, there are 12 inches in a foot)

25 x (67 x 67/703) = A healthy weight starts at 159.6 lbs

Step 2

After you have calculated the weight that puts you at a healthy BMI, now it is time to calculate your excess body weight.

Pre-op weight – weight to be at a BMI of 25 = Excess body weight

Example: Your pre-op weight was 320 lbs. and you are 5’7”

320 – 159.6 = 160.4 lbs of excess body weight

Step 3

To calculate the percentage excess body weight loss, use the following formula.

(Number of lbs you lost / excess body weight) x 100 = Percent of excess body weight loss

Example: Your excess body weight was 160.4 lbs; You lost 120 lbs from 320 lbs and your current weight is 200 lbs. 

(120 / 160.4) x 100 = You lost 74% of excess body weight 

That’s it!

With these calculations in place you will be able to better track your progress and continue to work toward your goals.

About this Blog

Learn about bariatric surgery and get the support you need to continue on your weight-loss journey. We offer workouts, recipes and tips from Bariatric Surgery program team members, and stories from patients like you.

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