Gastric Sleeve Weight Loss Calculator
Enter your height, weight, and sex to get a personalized gastric sleeve weight loss projection based on published clinical benchmarks. The calculator shows your ideal body weight (Devine formula), excess weight, and projected weight at 3, 6, 12, 18, and 24 months post-surgery as both kilograms (or pounds) and percentage of excess weight lost (%EWL). A timeline chart and step-by-step breakdown are included so you can see exactly how the numbers are reached.
How the gastric sleeve weight loss projection works
The calculator uses two published formulas. Your ideal body weight is estimated with the Devine formula: 50 kg plus 2.3 kg for every inch above 5 feet for men, and 45.5 kg plus 2.3 kg per inch for women. Excess weight is whatever you currently carry above that figure. Gastric sleeve (sleeve gastrectomy) patients lose a fraction of that excess weight at each milestone, based on weighted averages from clinical registries: 30% by 3 months, 50% by 6 months, 65% by 12 months, 68% by 18 months, and 70% by 24 months. These are population averages and your outcome will depend on diet, exercise, metabolic health, and surgical technique.
What %EWL and %TBWL mean
Percentage of excess weight loss (%EWL) measures how much of the weight above your ideal body weight has been shed. It is the standard metric used in bariatric research because it normalises for starting weight. Percentage of total body weight loss (%TBWL) is simpler - it is just the total weight dropped divided by your starting weight. A 120 kg patient with an IBW of 70 kg has 50 kg of excess weight. Losing 35 kg (70% EWL) is the same as a 29% TBWL. Surgeons and researchers typically report %EWL, but insurers and patients often find %TBWL easier to interpret.
Factors that affect your actual outcome
Published averages mask wide individual variation. People who follow a protein-first diet, stay active, attend follow-up appointments, and avoid high-calorie liquids consistently lose more than those who do not. Age matters too - patients under 50 tend to lose weight faster and regain less. Starting BMI is a double-edged factor: very high BMI patients have more excess weight to lose in absolute terms, but a lower %EWL on average. Hormonal conditions such as hypothyroidism or polycystic ovary syndrome can slow progress, while resolution of type 2 diabetes often begins within days of surgery due to gut hormone changes that are independent of weight loss.
How to use this calculator for post-operative tracking
Enter your weight before surgery (not your current post-op weight) to see the full projection curve from your starting point. If you want to check where you stand relative to the benchmark at a given milestone, note the calculator value for that month and compare it to your actual weight. Falling behind the curve at 6 months is not necessarily alarming - rapid weight loss slows as restriction adapts - but a plateau before 12 months that is significantly below benchmark is worth discussing with your bariatric team. The %EWL figure is more meaningful than raw kilograms because it accounts for how much weight you had to lose.
Expected %EWL by bariatric procedure at 12-18 months
| Procedure | Expected %EWL (12-18 mo) | Notes |
|---|---|---|
| Gastric sleeve (LSG) | 60-70% | Most common procedure globally |
| Gastric bypass (RYGB) | 70-80% | Slightly higher EWL, more complex |
| Duodenal switch | 75-85% | Highest EWL, highest complexity |
| Adjustable gastric band | 40-50% | Lowest EWL, reversible |
| Gastric balloon | 25-30% | Temporary, non-surgical |
Published clinical averages. Gastric sleeve (sleeve gastrectomy) is the most common bariatric procedure worldwide. Individual results vary significantly.
Frequently asked questions
How much weight will I lose with a gastric sleeve?
Clinical data shows gastric sleeve patients lose 60-70% of their excess weight in the first 18 months. Using the Devine ideal body weight formula, excess weight is the amount above your ideal weight for your height and sex. If you enter your starting weight and height, this calculator projects your weight at 3, 6, 12, 18, and 24 months based on those published averages.
What is %EWL and why is it used instead of total weight lost?
%EWL (percentage of excess weight loss) measures how much of the weight above your ideal body weight has been shed. It is preferred in bariatric research because it lets doctors compare outcomes fairly across patients of different starting sizes. Losing 40 kg means very different things for a person who started 50 kg above their ideal weight versus one who started 100 kg above it.
What is the Devine ideal body weight formula?
The Devine formula was published by B.J. Devine in 1974 and remains the most widely used bariatric reference. For men: IBW = 50 kg + 2.3 kg for each inch above 5 feet. For women: IBW = 45.5 kg + 2.3 kg per inch above 5 feet. It has known limitations for very short or very tall people but is consistently used across bariatric surgery research.
When does weight loss slow down after gastric sleeve surgery?
The fastest loss happens in the first 3-6 months, when restriction is greatest and caloric intake is lowest. Loss slows noticeably after 12 months and most patients reach their lowest weight around 18-24 months. Some regain 10-20% of lost weight between years 2 and 5, which is why long-term lifestyle habits are critical.
Can I use this calculator if I already had surgery?
Yes. Enter your pre-surgery starting weight and your height to generate the benchmark projection, then compare your actual current weight to the projected weight for the month you are in. This shows whether you are tracking ahead, on pace, or behind the clinical average for your milestone.
Is gastric sleeve better than gastric bypass for weight loss?
Gastric bypass (RYGB) typically produces slightly higher %EWL - around 70-80% versus 60-70% for sleeve - but it is a more complex surgery with a different risk profile. The sleeve is now the most commonly performed bariatric procedure worldwide because it offers a strong weight loss outcome with a simpler surgical technique and fewer long-term nutritional complications.