How to Calculate BMI (and What It Actually Tells You)
The formula
Body Mass Index is **BMI = weight (kg) / height (m)²**. A 175 cm, 70 kg adult has a BMI of 22.9. It's a screening tool, not a diagnostic.
The categories
- Under 18.5 — underweight
- 18.5 to 24.9 — normal
- 25 to 29.9 — overweight
- 30+ — obese
Where BMI is wrong
Muscle is denser than fat, so athletes routinely score "overweight" while carrying single-digit body fat. Older adults lose muscle without losing weight, so a "normal" BMI can hide sarcopenia. Kids and pregnant women need age- or trimester-specific charts.
A better pair of numbers
Combine BMI with waist circumference. A waist above 94 cm (men) or 80 cm (women) is a stronger predictor of metabolic risk than BMI alone.
What to do with the result
If you're outside the "normal" band, look at trend, not the single point. Weight moves 1–2 kg with hydration; a monthly average tells the truth.
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