What is BMI (Body Mass Index)?
Body Mass Index is a simple screening number that relates your weight to your height. It is calculated as your weight in kilograms divided by your height in meters squared (kg/m²). Doctors use it as a fast first indicator of whether you are in a healthy weight range — and, in bariatric medicine, as one of the criteria for who may benefit from weight-loss surgery.
BMI categories (WHO)
| BMI range | Category | What it usually means |
|---|---|---|
| Below 18.5 | Underweight | Below the healthy range |
| 18.5 – 24.9 | Normal weight | Healthy range |
| 25 – 29.9 | Overweight | Increased health risk |
| 30 – 34.9 | Obesity class I | May qualify for non-surgical or balloon programs |
| 35 – 39.9 | Obesity class II | Surgery candidate, especially with comorbidities |
| 40 and above | Obesity class III | Strong candidate for bariatric surgery |
What BMI do you need for weight-loss surgery?
International guidelines generally consider a person a candidate for bariatric surgery (such as gastric sleeve or gastric bypass) when BMI is 40 or higher, or 35–39.9 with an obesity-related condition such as type 2 diabetes, high blood pressure or sleep apnea. Newer metabolic-surgery criteria also support surgery from a BMI of 30–34.9 when type 2 diabetes is poorly controlled.
If your BMI is between 30 and 35 without serious comorbidities, a gastric balloon or our non-surgical Método 4 PRO program may be a better first step. The only way to know what fits your case is a medical evaluation.
Limitations of BMI
BMI is a screening tool, not a complete picture of health. It does not distinguish muscle from fat, so very muscular people can read as “overweight,” and it does not measure where fat is stored. Our team complements BMI with body-composition analysis (InBody), waist measurement, lab work and your medical history.
Frequently asked questions
What BMI do I need for bariatric surgery?
Usually a BMI of 40+, or 35+ with an obesity-related illness. Metabolic surgery may be considered from 30–35 with poorly controlled type 2 diabetes. Your surgeon confirms eligibility during the consultation.
Is BMI accurate?
It is an accurate population screening tool but an imperfect individual one. It ignores muscle mass and fat distribution, so we always pair it with a full clinical assessment.
How do I lower my BMI?
By reducing body weight through nutrition, activity and, when indicated, medical or surgical treatment. For higher BMI ranges, bariatric surgery is the most effective and durable option.
Does a high BMI mean I need surgery?
Not automatically. A high BMI is one signal among several. Some patients do best with a non-surgical program; others benefit from surgery. A personalized evaluation decides.