Medical disclaimer
This tool is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your health.
BMI Calculator Online - Calculate Your Body Mass Index
BMI (Body Mass Index) is an international measure used to check whether an adult's weight is healthy for their height. Formula: BMI = weight (kg) ÷ height² (m). Example: 70 kg ÷ (1.75 m)² = 22.9
BMI categories (WHO)
| Category | BMI range |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 - 24.9 |
| Overweight | 25 - 29.9 |
| Obesity Class I | 30 - 34.9 |
| Obesity Class II | 35 - 39.9 |
| Obesity Class III | ≥ 40 |
How to interpret BMI
BMI relates weight to height in adults. It does not distinguish muscle from fat — an athlete with high muscle mass may have “overweight” BMI while having low body fat. Older adults and pregnancy need careful interpretation; children use age- and sex-specific percentile charts, not adult cut-off values.
Clinical limitations
The calculator output is not a diagnosis or medical advice. If you have chronic conditions, take medications that affect weight, or worry about your weight — consult a clinician or registered dietitian. This text is educational only.
After you calculate BMI
- Waist circumference — complements BMI for metabolic risk (visceral fat).
- Habits — sustainable activity and diet matter more than one number.
- Trends — track over weeks, not day-to-day fluctuations.
- Prevention — follow screening advice from your GP for your age and sex.
FAQ — BMI calculator
Is BMI the same as body fat percentage?
No. BMI is weight/height²; body fat % needs different measurements (e.g. skinfold, DEXA) or formulas.
Why is my BMI “overweight” but I feel healthy?
BMI is a population-level metric. Individual health depends on body composition, fitness and labs — discuss with a doctor.
How often should I check BMI?
Occasionally when height is stable; monthly trends matter more than daily noise.