Enter your height and weight, pick any two procedures (sleeve, bypass, mini bypass, SADI-S, duodenal switch, SASI, band, balloon, plication or revisions) and see how much you could lose at 1, 3, 6, 12 and 18 months. Based on published %EWL data, reviewed by Dr. Alejandro López, board-certified bariatric surgeon.
Surgeons measure results as percentage of excess weight lost (%EWL). Your excess weight is the difference between your current weight and your ideal weight at a BMI of 25. The calculator multiplies that excess by the %EWL range each procedure achieves at each milestone in the published literature:
Ideal weight = 25 × height² · Excess weight = current weight − ideal weight · Expected loss = excess weight × %EWL
Example: a patient who is 5′8″ and 240 lb has an ideal weight of about 164 lb and 76 lb of excess weight. With a gastric sleeve (60–70% EWL at 12 months) the expected loss is 45–53 lb in the first year; with a gastric bypass (65–75%) it is 49–57 lb. Results are shown as ranges because real patients vary with age, starting BMI, comorbidities and — above all — adherence to the post-op program.
Typical %EWL at 12 and 18 months for primary (first-time) bariatric procedures, with the pounds a 240-lb, 5′8″ patient (76 lb of excess weight) would expect to lose in the first year.
| Procedure | %EWL at 12 months | %EWL at 18 months | Example: lb lost at 12 months |
|---|---|---|---|
| Gastric sleeve | 60–70% | 65–75% | 46–53 lb |
| Gastric bypass (RYGB) | 65–75% | 70–80% | 49–57 lb |
| Mini gastric bypass | 70–85% | 75–85% | 53–65 lb |
| SADI-S | 75–85% | 80–90% | 57–65 lb |
| Duodenal switch | 75–85% | 80–90% | 57–65 lb |
| SASI bypass (transit bipartition) | 75–85% | 78–88% | 57–65 lb |
| Gastric band (Lap-Band®) | 40–50% | 42–52% | 30–38 lb |
| Gastric balloon (temporary, 6 months) | 25–35% | — | 19–27 lb |
| Gastric plication | 35–45% | 30–45% | 27–34 lb |
If you already had a band, sleeve or bypass and regained weight, a conversion (revision) still produces meaningful loss — but usually less than a first surgery, because part of your excess weight was already lost. These ranges are measured from your weight at the time of the revision.
| Revision (from → to) | %EWL at 12 months | %EWL at 18 months |
|---|---|---|
| Band → Sleeve | 50–62% | 52–65% |
| Band → Bypass | 52–65% | 55–68% |
| Sleeve → Bypass (RYGB) | 45–58% | 48–62% |
| Sleeve → SADI-S | 55–68% | 58–72% |
| Sleeve → Duodenal switch | 58–72% | 60–75% |
| Bypass → Distal bypass | 40–52% | 42–55% |
| Re-sleeve | 32–45% | 34–48% |
Weight loss is fastest in the first three months and slows as you approach your new weight. For a patient with about 75 lb of excess weight, the typical pace looks like this:
| Period | Gastric sleeve | Gastric bypass | SADI-S / Duodenal switch |
|---|---|---|---|
| Month 1 | 8–11 lb | 9–14 lb | 11–15 lb |
| Months 2–3 (per month) | 5–8 lb | 6–8 lb | 7–10 lb |
| Months 4–6 (per month) | 5–6 lb | 5–6 lb | 5–6 lb |
| Months 7–12 (per month) | 2–3 lb | 2–3 lb | 2–4 lb |
| Months 13–18 (per month) | ≈1 lb | ≈1 lb | ≈1 lb |
| Total at 12 months | 45–53 lb | 49–57 lb | 57–65 lb |
On average the gastric bypass loses about 5% more excess weight than the gastric sleeve at 12 months (65–75% vs 60–70%) and keeps a small edge at 18 months. The bypass also controls acid reflux and type 2 diabetes more reliably, while the sleeve is a simpler operation with no intestinal rerouting and a lower risk of nutritional deficiencies. Mini gastric bypass and SADI-S sit in between in complexity and above both in weight loss. Use the “Sleeve vs Bypass” quick comparison above, or read our full bariatric surgery comparison for costs, risks and who each procedure fits.
It gives a realistic range, not a promise. The ranges come from published studies and registry averages; about two thirds of patients land inside them, and the rest fall a little above or below depending on starting BMI, age, medical conditions and how closely they follow the diet, protein and activity plan.
It is the share of your excess weight that you lose. Excess weight is your current weight minus your ideal weight at a BMI of 25. If you have 100 lb of excess weight and lose 65 lb, your %EWL is 65%. Surgeons also use %TBWL (percentage of total body weight lost); a sleeve typically achieves 25–30% TBWL at one year.
Most patients lose 60–70% of their excess weight in the first 12 months and 65–75% by 18 months. With 76 lb of excess weight that is 45–53 lb in the first year. See the gastric sleeve weight loss calculator for a month-by-month timeline.
Typically 65–75% of excess weight at 12 months and 70–80% at 18 months — roughly 5% more than the sleeve. A 300-lb patient at 5′4″ (about 154 lb of excess weight) could expect to lose 100–116 lb in the first year.
Yes. Higher-BMI patients lose more pounds in absolute terms but often a slightly lower percentage of excess weight; that is why SADI-S or a duodenal switch are frequently recommended above a BMI of 50. Enter your own numbers in the calculator to see the effect.
Most of the loss happens in the first 12 months; it slows through month 18 and stabilizes around 18–24 months. Long-term maintenance depends on habits, follow-up and, in some cases, medication or revision surgery.
Usually less, because part of the excess weight was already lost after the original operation. Conversions to SADI-S or duodenal switch produce the largest additional loss (55–72% EWL), while a re-sleeve produces the least (32–45%).
Ranges in this tool are estimates based on the literature above and ALO Bariatrics’ clinical experience. Individual results vary. This calculator is educational and is not a medical diagnosis or a guarantee of results.
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