Calculating Body Mass Index

Body Mass Index is not just about how much you weight, but also takes your height into consideration

You will need to know your Body Mass Index (BMI) to find out if you're eligible for surgery.

The Body Mass Index is your weight in kilograms divided by the square of your height in meters. You may be eligible if your BMI is over 40 (morbid obesity) or over 35 with a serious obesity-related health condition, such as uncontrolled Type 2 diabetes, sleep apnea or severe joint pain that limits your daily activities. 

Understanding weight loss metrics

Using the metrics of Excess Body Weight (EBW) and Excess Weight Loss (EWL) helps us to understand how much weight loss we should expect relative to our height.

You might hear that someone has lost 50 pounds, but without calculating their EBW and EWL there is no way of determining if they have lost a lot or a little amount of weight relative to their body height. If the person who lost those 50 pounds is taller than you and has hundreds of pounds more to lose than you, 50 pounds isn't that much weight to lose. However, if the person only had 50 pounds to lose, we can confirm that person lost 100 per cent EWL and have reached their weight loss target!


In the UK it is customary to measure body weight in pounds. For instance, a person weighing 250 pounds might have a goal of losing 100 pounds to reach a target weight 150 pounds. When measuring weight loss using BMI metrics it is important to compare weight and weight loss goals with body height. For this reason Excess Body Weight (EBW) and Excess Weight Loss (EWL) are often used.

Excess Body Weight

EBW is the amount of body weight you have in excess of your target weight. The normal BMI range is about 24. The ideal body weight for a person of a height of 5 feet 7 inches is about 150 pounds. If you weigh 250 pounds then we calculate your EBW to be 100 pounds. 

Excess Weight Loss

EWL is the percentage of your EBW that you lose. We calculate EWL by dividing the number of pounds lost by the amount of pounds in your EBW. For example, if your EBW is 100 pounds and you lose 45 pounds, your EWL is 45 per cent. 


Please seek and follow the specific guidelines from your bariatric team. Guidelines vary for individual patient needs and surgeries.


Calculate your BMI