Free tool
BMI calculator
The body mass index (BMI) puts your weight in relation to your height and gives you a first idea of where you stand. Simply enter your height and weight — your result appears instantly.
Want to find out straight away whether a doctor-led treatment could be an option for you?
Your BMI
–kg/m²
Enter your height and weight — your result will appear here.
| Category | BMI range |
|---|---|
| Underweight | below 18.5 |
| Normal weight | 18.5–24.9 |
| Overweight | 25–29.9 |
| Obesity | 30 and above |
What is the BMI?
The body mass index (BMI) puts your body weight in relation to your height. The formula: weight in kilograms divided by height in metres squared (kg/m²). At 170 cm and 82.5 kg, for example, that gives a BMI of 28.5. The World Health Organization (WHO) and medical societies have used the value for decades to roughly classify weight — as a quick screening value that is calculated the same way everywhere.
That is also exactly where its limits lie: the BMI does not measure what your weight is made of. It does not distinguish between muscle and fat mass, takes neither age nor sex into account and says nothing about fat distribution — even though where fat sits makes a difference to health. Athletic people with a lot of muscle mass can have a high BMI with low body fat. The BMI is therefore a starting point for a conversation — not a diagnosis.
The BMI categories
For adults, the WHO classification into four ranges applies. It is deliberately coarse and applies regardless of age and sex — the transitions are fluid, and what a value means for you personally depends on your overall situation.
| Category | BMI range |
|---|---|
| Underweight | below 18.5 |
| Normal weight | 18.5–24.9 |
| Overweight | 25–29.9 |
| Obesity | 30 and above |
Lowering your BMI: why willpower often is not enough
If losing weight were purely a question of discipline, there would hardly be any excess weight. In reality the body fights weight loss: hormones such as ghrelin and leptin control hunger and satiety, and after dieting the hunger signal is often stronger than before — one reason many people experience the well-known yo-yo effect. Genetics, medication, sleep and stress play a part too.
That does not mean nutrition and exercise do not matter — they remain the basis of any weight loss. But it explains why willpower alone often is not enough and why repeated setbacks are not a personal failure. For people with significant excess weight there are now doctor-led treatments that target exactly these mechanisms: they influence hunger and satiety and are combined with dietary changes and more exercise.
When a doctor-led treatment can be an option
A doctor-led weight-loss treatment is not a lifestyle product — it is intended for people whose health is burdened by excess weight. A conversation about it is worthwhile, for example, if one or more of these points apply to you:
- You have lost weight several times and it came back (yo-yo effect).
- Losing weight is getting noticeably harder as you get older.
- You have weight-related conditions such as high blood pressure, prediabetes or sleep apnoea.
- You have a hormonal cause such as PCOS or a thyroid condition.
Find out whether a treatment could be an option for you
The medical questionnaire takes a few minutes, is free of charge and without obligation. A doctor reviews your answers — a treatment only goes ahead if it is medically suitable.
Check suitability nowFrom which BMI is a treatment possible?
Usual BMI ranges from licensing and guidelines apply to the different treatment paths. They are reference values — not an automatic yes, and no substitute for the individual assessment:
| Treatment path | Usual BMI range |
|---|---|
| Doctor-led GLP-1 treatment | from BMI 30, or from BMI 27 with a weight-related condition |
| Bariatric surgery | usually from BMI 40, or from BMI 35 with a related condition |
We mention surgery here for context only — it belongs in specialised centres; talk to your doctor about it. Whether a GLP-1 treatment is possible for you is assessed at saelf by a doctor based on the medical questionnaire.
Frequently asked questions about the BMI
What is the BMI?
The body mass index puts your weight in relation to your height (kg/m²). It is a screening value that roughly classifies weight into categories such as normal weight, overweight and obesity — but it measures neither body composition nor fat distribution and does not replace a medical assessment.
How do I calculate my BMI?
Divide your weight in kilograms by your height in metres squared. Example: 82.5 kg at 1.70 m gives 82.5 ÷ (1.70 × 1.70) = BMI 28.5. Or simply use the calculator at the top of this page — it calculates automatically as soon as you enter your height and weight.
From which BMI is a treatment possible?
Modern GLP-1-based weight-loss treatments are usually intended from a BMI of 30, or from 27 with a weight-related condition such as high blood pressure or type 2 diabetes — always alongside dietary changes and exercise. Whether a treatment is individually suitable for you is assessed by a doctor based on the medical questionnaire.