BodyCalThe healthy range: 18.5 to 24.9
Body Mass Index is your weight in kilograms divided by your height in metres squared. The World Health Organization classifies a BMI of 18.5–24.9 as the healthy range, 25–29.9 as overweight, and 30+ as obese. These cutoffs come from large population studies linking BMI ranges to disease and mortality risk.
At the population level, BMI is a remarkably useful screening tool — it correlates well with body fat for most adults and predicts risk of type 2 diabetes, heart disease, and several cancers.
Where BMI gets it wrong
BMI cannot tell muscle from fat. A muscular athlete can register as 'overweight' while carrying very little body fat; an older adult with low muscle mass can have a 'healthy' BMI while carrying excess visceral fat. It also doesn't capture where fat is stored — abdominal fat is far more metabolically harmful than fat on the hips and thighs.
That's why clinicians increasingly pair BMI with waist circumference, waist-to-height ratio, or body composition measurements before drawing conclusions.
How to use your BMI number
Treat BMI as a conversation starter, not a verdict. If your BMI falls outside the healthy range and you also have a high waist measurement, low energy, or risk factors like elevated blood pressure, it's worth talking to a healthcare provider. If you're an athlete with a BMI of 26 and visible abs, your number is almost certainly noise.
Check your BMI a few times per year rather than daily — it changes slowly and is most meaningful as a long-term trend.