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⚖️ BMI Calculator

Calculate your Body Mass Index and see your weight category.

How BMI is calculated

Body Mass Index divides your weight in kilograms by your height in metres squared. If you enter pounds and inches, the calculator converts them first, so the result is identical either way.

BMI = weight (kg) ÷ height (m)²

The World Health Organization uses four adult categories: under 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight, and 30 or above is classified as obese. Those thresholds are the same for men and women.

What BMI does not tell you

BMI was designed in the 19th century to describe populations, not individuals, and it has a well-known blind spot: it cannot distinguish muscle from fat. A rugby player and a sedentary person of the same height and weight get the same number, even though their body composition is nothing alike. Athletes routinely land in the "overweight" band while carrying very little fat.

It also ignores where fat sits. Fat around the abdomen carries more metabolic risk than fat on the hips and thighs, which is why many clinicians now look at waist circumference alongside BMI. A waist over 40 inches in men or 35 inches in women is treated as a warning sign regardless of what BMI says.

Finally, the standard thresholds were derived largely from European populations. Health authorities in several Asian countries use lower cut-offs, because cardiometabolic risk begins to rise at a lower BMI in those groups.

Using the number sensibly

BMI is most useful as a starting point and a trend line. A single reading tells you roughly which band you sit in; tracking it over months tells you whether things are moving. If your BMI sits just outside the healthy range and you are otherwise active with normal blood pressure and blood sugar, the number alone is not a reason to panic.

If you want a fuller picture, pair BMI with a waist measurement, a body fat estimate, and — if you are planning changes to your diet — a daily calorie estimate.

Common questions

Is BMI accurate for children?
Not with adult thresholds. Children are assessed with age- and sex-specific percentile charts, because body composition changes rapidly during growth. This calculator is intended for adults.
Does BMI change with age?
The formula does not, but body composition does. Muscle mass tends to decline after roughly age 50, so an unchanged BMI can hide a gradual shift toward more fat and less muscle.
What is a healthy rate of change?
Most guidance points to around 0.5 to 1 kg per week as a sustainable rate. Faster changes tend to come disproportionately from water and lean tissue rather than fat.
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