Who qualifies for weight loss surgery?

Standard eligibility criteria: BMI ≥40, or BMI ≥35 with at least one obesity-related comorbidity (type 2 diabetes, sleep apnea, hypertension, etc.), or BMI 30–35 with poorly controlled type 2 diabetes (for metabolic surgery). You must also have documented failure of non-surgical weight loss attempts. Some programs require a 6-month supervised diet before approval. Insurance requirements vary by provider.

What is the safest bariatric surgery?

All three procedures are generally safe when performed by experienced surgeons at accredited centers. The 30-day mortality rate is approximately 0.1–0.3% for all procedures. Sleeve gastrectomy has slightly lower short-term complication rates than gastric bypass. Gastric band has low surgical risk but higher long-term revision rates (up to 50% at 10 years). Overall, sleeve gastrectomy is currently considered the best balance of effectiveness and safety.

How fast do you lose weight after bariatric surgery?

Weight loss is fastest in the first 6 months: typically 3–5 lbs/week for bypass, 2–4 lbs/week for sleeve, and 1–2 lbs/week for band. Weight loss slows significantly after 6 months and typically plateaus at 12–18 months for bypass/sleeve and 18–24 months for band. Most patients reach their nadir (lowest weight) at 12–18 months post-surgery.

Can you regain weight after bariatric surgery?

Yes. Weight regain is common, particularly after 2–5 years. Studies show 20–30% of patients regain significant weight (>50% of lost weight) within 5–10 years. Factors that contribute: stretching of the gastric pouch/sleeve, hormonal adaptation, return to high-calorie eating patterns, and decreased physical activity. Long-term dietary compliance and regular follow-up with your bariatric team are essential for maintaining results.

What are the nutritional consequences of bariatric surgery?

All procedures require lifelong vitamin and mineral supplementation. Gastric bypass has the highest risk of nutritional deficiencies (iron, B12, calcium, vitamin D, folate) due to malabsorption. Sleeve has moderate risk. Band has the lowest nutritional impact but still requires monitoring. Protein intake of 60–80g/day is essential for all procedures. Most patients need to eat 4–6 small meals daily rather than 3 large meals.

What health conditions improve after bariatric surgery?

Type 2 diabetes remission: 60–80% (bypass), 50–70% (sleeve), 30–50% (band). Hypertension improvement: 60–70% of patients. Sleep apnea resolution: 70–80%. GERD: improves with bypass, may worsen with sleeve. Joint pain significantly reduces. Fertility often improves. Depression symptoms improve in 50–60% of patients. Overall, bariatric surgery reduces 10-year mortality by approximately 30–40%.

Weight Loss Surgery Comparison Calculator

Compare bariatric surgery options: gastric bypass, sleeve gastrectomy, and gastric band. See expected weight loss, timelines, and eligibility by BMI.

Current Weight

lbs

Height (ft)

Height (in)

Current BMI

45.6

Ideal Weight (BMI 25)

164 lbs

Excess Weight

136 lbs

Eligible: BMI ≥40

Gastric Bypass (RYGB)

Expected loss: 82–109 lbs

Final weight: 191–218 lbs

Final BMI: 29–33.1

EWL: 60–80%

Peak: ~15 months

Avg EWL: 70%

Sleeve Gastrectomy (VSG)

Expected loss: 68–95 lbs

Final weight: 205–232 lbs

Final BMI: 31.2–35.3

EWL: 50–70%

Peak: ~15 months

Avg EWL: 60%

Gastric Band (LAGB)

Expected loss: 54–75 lbs

Final weight: 225–246 lbs

Final BMI: 34.2–37.4

EWL: 40–55%

Peak: ~24 months

Avg EWL: 48%

Side-by-Side Comparison

Factor	Gastric Bypass	Sleeve Gastrectomy	Gastric Band
Weight Loss (lbs)	82–109	68–95	54–75
EWL%	60–80%	50–70%	40–55%
Peak Weight Loss	~15 months	~15 months	~24 months
Diabetes Remission	60–80%	50–70%	30–50%
Complication Rate	10–15%	5–10%	5–8%
Reversible	Technically yes, rarely done	No (stomach removed)	Yes (fully)

⚠ Important: These are population-level averages. Individual results depend on compliance with post-surgical dietary guidelines, exercise, metabolic factors, and ongoing medical care. This calculator is for informational purposes only — it does NOT replace a surgical consultation.

Disclaimer: Bariatric surgery is a major medical decision. This calculator provides estimates based on published clinical outcomes and is NOT medical advice. Consult a board-certified bariatric surgeon for eligibility evaluation, procedure selection, and personalized outcome expectations.

Planning notes, formulas, and examples

About the Weight Loss Surgery Comparison Calculator

Bariatric surgery is the most effective long-term treatment for severe obesity, but choosing the right procedure requires understanding the differences in expected outcomes, risks, recovery, and lifestyle changes. The three most common procedures — Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (VSG), and adjustable gastric band (LAGB) — each offer different profiles of weight loss effectiveness, complication rates, and reversibility.

Weight loss after bariatric surgery is measured in Excess Weight Loss percentage (EWL%), calculated as the percentage of weight above a BMI of 25 that is lost. At 2 years post-surgery, typical results are: gastric bypass 60–80% EWL, sleeve gastrectomy 50–70% EWL, and gastric band 40–55% EWL.

This calculator helps you compare expected outcomes across all three procedures based on your current BMI, providing realistic timelines and helping you have an informed discussion with your bariatric surgeon.

When This Page Helps

Choosing bariatric surgery is life-changing. It shows a side-by-side comparison of typical outcomes so you can review the tradeoffs before discussing the options with your surgical team.

How to Use the Inputs

Enter your current weight and height to calculate BMI.
Review your eligibility status for bariatric surgery.
Compare expected weight loss across the three surgery types.
See the projected timeline for weight loss milestones.
Review additional health improvement estimates.
Discuss results with your bariatric surgeon for personalized guidance.

Formula used

BMI = weight(kg) / height(m)²
Excess Weight = Current Weight − Weight at BMI 25
EWL% = (Weight Lost / Excess Weight) × 100

Typical EWL% by Procedure (2-year outcomes):
• Gastric Bypass (RYGB): 60–80% EWL
• Sleeve Gastrectomy (VSG): 50–70% EWL
• Gastric Band (LAGB): 40–55% EWL

Eligibility:
• BMI ≥40 (or ≥35 with obesity-related comorbidities)
• Failed prior non-surgical weight loss attempts

Example Calculation

Result: BMI 45.6 | Excess weight: 135 lbs | Bypass: 81–108 lbs | Sleeve: 68–95 lbs | Band: 54–74 lbs

At 300 lbs and 5'8", BMI is 45.6 with 135 lbs of excess weight (above BMI 25 = 165 lbs). Gastric bypass at 60–80% EWL = 81–108 lbs lost, reaching 192–219 lbs. Sleeve at 50–70% EWL = 68–95 lbs lost, reaching 205–232 lbs. Band at 40–55% EWL = 54–74 lbs lost, reaching 226–246 lbs. These results typically occur over 12–24 months with peak weight loss at 12–18 months for bypass/sleeve.

Tips & Best Practices

EWL percentages are averages — individual results vary based on diet compliance, exercise, genetics, and starting BMI.
Gastric bypass has the highest average weight loss but also the most complex surgery and largest nutritional impact.
Sleeve gastrectomy has become the most popular procedure due to good outcomes with lower complexity than bypass.
The gastric band has fallen out of favor due to lower effectiveness and high long-term complication/revision rates.
All procedures require lifelong dietary changes, vitamin supplementation, and medical follow-up.
Weight regain of 10–20% from nadir (lowest weight) is common at 5+ years regardless of procedure — maintenance matters.

Understanding Excess Weight Loss (EWL%)

EWL% is the standard metric for bariatric surgery outcomes, not total weight loss. It's calculated as: (Weight Lost / Excess Weight) × 100, where excess weight is everything above a BMI of 25. A patient starting at 300 lbs with an ideal weight of 165 lbs has 135 lbs of excess weight. If they lose 95 lbs (reaching 205 lbs), their EWL% is 70%. This metric allows fair comparison across patients of different starting sizes.

Procedure Comparison at a Glance

Gastric bypass creates a small stomach pouch and reroutes the intestines, causing both restriction and mild malabsorption. It has the highest weight loss but is the most complex surgically. Sleeve gastrectomy removes ~80% of the stomach, creating a banana-shaped tube. It's restriction-only with no intestinal rerouting. The gastric band places an adjustable silicone ring around the upper stomach to limit food intake. It's the least invasive but least effective.

Making the Decision

No single procedure is best for everyone. Your bariatric surgeon will consider: your BMI, medical conditions (especially diabetes and GERD), eating patterns, surgical history, and personal preferences. The best surgery is the one that your surgical team recommends based on YOUR specific medical profile and that you can commit to following long-term.

Sources & Methodology

Last updated: March 28, 2026

Methodology

This worksheet applies a simple excess-weight-loss framework to compare common bariatric procedures side by side. It is designed to compare planning assumptions, not to decide surgical eligibility or forecast a specific operative result.

Sources

Bariatric Surgery for Adults (National Institute of Diabetes and Digestive and Kidney Diseases) — NIDDK overview of bariatric surgery options, risks, and expected outcomes.
Choosing a Safe & Successful Weight-loss Program (National Institute of Diabetes and Digestive and Kidney Diseases) — NIDDK guidance on realistic weight-management planning and follow-up.
Healthy Weight, Nutrition, and Physical Activity (Centers for Disease Control and Prevention) — CDC overview of weight-management context and healthy weight maintenance.

Frequently Asked Questions

Standard eligibility criteria: BMI ≥40, or BMI ≥35 with at least one obesity-related comorbidity (type 2 diabetes, sleep apnea, hypertension, etc.), or BMI 30–35 with poorly controlled type 2 diabetes (for metabolic surgery). You must also have documented failure of non-surgical weight loss attempts. Some programs require a 6-month supervised diet before approval. Insurance requirements vary by provider.
All three procedures are generally safe when performed by experienced surgeons at accredited centers. The 30-day mortality rate is approximately 0.1–0.3% for all procedures. Sleeve gastrectomy has slightly lower short-term complication rates than gastric bypass. Gastric band has low surgical risk but higher long-term revision rates (up to 50% at 10 years). Overall, sleeve gastrectomy is currently considered the best balance of effectiveness and safety.
Yes. Weight regain is common, particularly after 2–5 years. Studies show 20–30% of patients regain significant weight (>50% of lost weight) within 5–10 years. Factors that contribute: stretching of the gastric pouch/sleeve, hormonal adaptation, return to high-calorie eating patterns, and decreased physical activity. Long-term dietary compliance and regular follow-up with your bariatric team are essential for maintaining results.
All procedures require lifelong vitamin and mineral supplementation. Gastric bypass has the highest risk of nutritional deficiencies (iron, B12, calcium, vitamin D, folate) due to malabsorption. Sleeve has moderate risk. Band has the lowest nutritional impact but still requires monitoring. Protein intake of 60–80g/day is essential for all procedures. Most patients need to eat 4–6 small meals daily rather than 3 large meals.
Type 2 diabetes remission: 60–80% (bypass), 50–70% (sleeve), 30–50% (band). Hypertension improvement: 60–70% of patients. Sleep apnea resolution: 70–80%. GERD: improves with bypass, may worsen with sleeve. Joint pain significantly reduces. Fertility often improves. Depression symptoms improve in 50–60% of patients. Overall, bariatric surgery reduces 10-year mortality by approximately 30–40%.