BMI Calculator (Body Mass Index)

How it works

Body Mass Index (BMI) is a screening tool that estimates body fat based on height and weight. It is calculated as weight in kilograms divided by height in meters squared. The World Health Organization defines four categories: underweight (BMI under 18.5), healthy weight (18.5–24.9), overweight (25–29.9), and obese (30 and over).

BMI is widely used because it is simple, cheap, and population-level data shows it correlates with obesity-related health risks like cardiovascular disease, type 2 diabetes, and certain cancers. For most adults of average build, BMI provides a useful first-pass risk indicator.

That said, BMI has well-known limitations for individuals. It does not distinguish between muscle and fat, so muscular athletes can register as "overweight" or even "obese" by BMI while having very low body fat. Conversely, someone with low muscle mass and excess body fat ("skinny fat") may have a normal BMI but elevated health risk. BMI also does not account for fat distribution — visceral fat (around organs) is more dangerous than subcutaneous fat — and may misclassify older adults, who tend to lose muscle mass while gaining fat.

For these reasons, BMI is best used as one data point among several. Waist circumference, body fat percentage, blood pressure, fasting blood glucose, and lipid panels together give a far more complete picture of metabolic health than BMI alone.

The healthy-weight range shown by this calculator (18.5–24.9 BMI) is for adults 20 and older. Children and teens use age- and sex-specific BMI percentiles. Pregnant and nursing women, and certain ethnic groups (where Asian populations may have elevated risk at lower BMIs), should consult their healthcare provider for guidance specific to them.