Body Mass Index (BMI)

Body mass index (BMI) is a number calculated from your weight in kilograms divided by the square of your height in metres. It is a quick screening measure used to classify weight and to decide who qualifies for weight loss treatment.

It is useful for populations and as a first step for individuals. It does not measure body fat directly, so it can mislead in very muscular people, older adults with muscle loss, and some ethnic groups who carry health risk at lower values.

What Body Mass Index (BMI) shows

BMI places adults into bands: under 18.5 underweight, 18.5 to 24.9 healthy range, 25 to 29.9 overweight, 30 to 34.9 obesity class 1, 35 to 39.9 class 2, and 40 or above class 3. Risk of type 2 diabetes, high blood pressure, sleep apnoea, fatty liver and joint disease rises through these bands. For people of South Asian, Chinese and some other backgrounds, lower action points of 23 and 27.5 are often used. In a bariatric assessment, BMI is read together with waist circumference, body composition and weight-related illnesses.

When Body Mass Index (BMI) is recommended

• Any adult health check
• Before considering weight loss medicines or bariatric surgery
• Monitoring progress after weight loss treatment
• Assessing anaesthetic and surgical risk before any operation
• Children, using age and sex specific centile charts rather than adult bands

Limits and situations where another test is better:

• Athletes and very muscular people may be classed as overweight without excess fat
• It does not show where fat is carried; waist measurement adds this
• Not valid in pregnancy
• Less reliable in older adults and in people with fluid retention or amputations

How to prepare

• Be weighed in light clothing without shoes, ideally in the morning
• Have height measured properly rather than relying on memory
• Bring a list of medical conditions and medicines if the visit is a bariatric assessment

What happens during the test

Height is measured with a wall-mounted stadiometer and weight on calibrated scales; the calculation is instant. Many clinics add a waist measurement and a bioimpedance body composition reading, where you stand barefoot on a platform holding handles for about a minute while a tiny, imperceptible current estimates fat and muscle mass.

Results and next steps

The result is available immediately. For bariatric surgery, international criteria are broadly a BMI of 40 or more, or 35 or more with a weight-related illness, and in some guidelines 30 to 35 with poorly controlled type 2 diabetes. A gastric balloon is usually considered from a BMI of about 27 to 30. The doctor then arranges blood tests, endoscopy and other assessments as needed.

• Test time: 5 minutes
• Results ready: Immediately
• Back to everyday activity: None

Safety and risks

• None from the measurement itself
• Misclassification if BMI is used alone
• Bioimpedance scales are generally avoided in people with pacemakers

Arranging Body Mass Index (BMI) in Türkiye

You do not need to travel to find out your BMI: calculate it at home and send it with your enquiry so the team can advise whether you meet criteria before you book anything. It is measured again in person at the pre-operative assessment, since home scales and remembered heights are often wrong.

Send your previous reports and the question you want answered and a Clinic-Y coordinator replies within 24 hours with suitable teams and written, all-inclusive proposals side by side. Reviewing your case is free.

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