Gastric Sleeve Weight Loss Calculator

Background.

After a sleeve gastrectomy the scale gives you one number, but bariatric teams usually talk in percentages. A 30 kg loss means something different for a patient who started at 130 kg than for one who started at 200 kg, so outcomes are expressed relative to where you began: as a share of total starting weight, or as a share of excess weight, the amount above a reference weight chosen for your height.

Percentage of excess weight lost, %EWL, is the older and still widely quoted measure. It asks how much of the gap between your starting weight and the reference has closed. Start at 130 kg with a reference of 70 kg and the excess is 60 kg; lose 30 kg and half of it has gone, 50% EWL. Percentage of total weight lost, %TWL, simply divides the loss by the starting weight: 30 ÷ 130, a little over 23%.

The two can tell different stories. %EWL depends on the reference weight, which is a convention rather than a measurement, and programmes choose it differently — the weight at a BMI of 25 for your height is a common choice. It also favours people who started closer to the reference: the same 30 kg lost from 100 kg against a 70 kg reference is 100% EWL. %TWL avoids both problems, which is why many surgical reports now give it alongside %EWL. All three figures appear here so you can match whichever your team uses.

The numbers describe progress; they do not forecast it. How much weight a sleeve patient loses, and how much returns in later years, varies widely with eating patterns, activity, metabolism and follow-up care. A figure lower than you hoped is something to raise with your bariatric team, not a verdict, and nothing here sets a healthy target weight or bears on whether surgery is right for you.

What is gastric sleeve weight loss calculator?

Excess weight loss (%EWL) is the share of your pre-surgery excess weight that has been lost, where the excess is pre-surgery weight minus a reference weight you supply. At 100% you have reached the reference weight; above 100% you are below it, and a negative value means you now weigh more than before surgery. Total weight loss is also given in kilograms and as a percentage of pre-surgery weight.

How to use this calculator.

1. 01Enter your pre-surgery weight in kilograms. Programmes differ on which weighing counts — the day of surgery or the start of the pre-operative diet — so use the one your team records, or your %EWL will not match theirs.
2. 02Enter your current weight in kilograms, ideally from the same scale at the same time of day each time you check.
3. 03Enter the reference weight your bariatric team uses. If you have not been given one, the weight at a BMI of 25 is a common convention: 25 × height in metres squared, so 1.70 m gives 25 × 1.70 × 1.70 = 72.25 kg.
4. 04Read %EWL, then look at the kilograms lost and %TWL, which do not depend on the reference weight at all.

The formula.

%EWL = (W₀ − W) ÷ (W₀ − W_ref) × 100, where W₀ is pre-surgery weight, W is current weight and W_ref is the reference weight, all in kilograms. The numerator is the weight lost; the denominator is the excess weight at the start. Alongside it, total weight lost is W₀ − W in kilograms, and %TWL = (W₀ − W) ÷ W₀ × 100. The reference weight is never estimated from height or anything else: it is whatever you enter, and it must be below the pre-surgery weight, because otherwise there is no excess to lose and the page refuses the input. The choice of reference moves %EWL a good deal. Raising it shrinks the denominator, so the same loss scores higher, while the kilograms and %TWL stay exactly where they were.

A worked example.

Frequently asked questions.

References& sources.

1. [1]American Society for Metabolic and Bariatric Surgery. Outcome reporting context current 2026. Weight-loss outcome terminology. Retrieved 2026-08-06.
2. [2]U.S. National Library of Medicine. PubMed record current 2026-08-06. Indexed derivation and validation literature. Retrieved 2026-08-06.
3. [3]World Health Organization. Patient safety resources current 2026. Clinical decision-support safety context. Retrieved 2026-08-06.