BMI calculator: a quick number with very real limits

Body Mass Index is the single most popular health metric on the internet. It is also one of the most over-interpreted. Here's everything you need to use it correctly — and the moment to stop using it.

Open the BMI calculator to try your own numbers.

The formula

BMI = weight (kg) / height (m)²

Example: 70 kg, 1.75 m → BMI = 70 / 3.0625 = 22.86 (normal).

That's it. No body-fat measurement, no muscle mass, no age, no sex, no waist circumference. Just two numbers in, one number out.

The categories (WHO, adults)

A few things to know:

• South Asians have different cut-offs. The Indian Council of Medical Research (ICMR) uses 23 (overweight) and 25 (obese) instead of 25 and 30. South Asians develop metabolic issues at lower BMIs than Europeans on average.
• Children and teens use age-and-sex-specific percentile charts, not the adult cut-offs.
• Athletes routinely score "overweight" by BMI because muscle is denser than fat. A bodybuilder at 90 kg and 1.80 m has BMI 27.8 — "overweight" — with possibly under 8% body fat.

When BMI is fine

• Population-level screening (public health, insurance actuarial work)
• Tracking changes in your own body over time
• A quick first-pass health flag for an average sedentary adult

When BMI is not fine

• Athletes, bodybuilders, anyone with above-average muscle mass
• Elderly people (sarcopenia distorts the ratio)
• Pregnant women
• Anyone of South Asian descent using European cut-offs
• Children and teens

In all these cases, body fat percentage (calculator here) or waist-to-height ratio is more informative.

A better one-line summary

BMI is a useful starting point and a terrible verdict.

Use it. Don't worship it. If the number concerns you, talk to a doctor — they have the bloodwork, history, and physical exam that one ratio could never capture.

Run yours

Open the BMI Calculator, enter your height and weight, and see where you land. Then read the health overview for what comes next.