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What Is a Healthy BMI? How to Calculate and Read Your Result

Body mass index (BMI) is a quick screening number that compares weight to height. Here’s what the ranges mean – and what BMI can’t tell you.

⚖️Free BMI Calculator
Body mass index in metric or US units, with healthy range.Open tool →

How BMI is calculated

BMI = weight in kilograms ÷ (height in metres)². In US units: 703 × weight in pounds ÷ (height in inches)². The BMI Calculator does both and shows your healthy weight range.

Adult categories

Under 18.5: underweight. 18.5-24.9: healthy weight. 25-29.9: overweight. 30 and above: obesity. Some health bodies use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds.

Where BMI falls short

It can't tell muscle from fat, so athletes may score 'overweight'. It doesn't show where fat is stored, and it isn't designed for children, pregnancy or older adults losing muscle.

Better together

Waist measurement (or waist-to-height ratio, ideally under 0.5), blood pressure and blood tests give a fuller picture. For health decisions, talk to a doctor.

Frequently asked questions

Is BMI accurate?

It's a reasonable population screening tool but can mislead for individuals.

Is a BMI of 25 bad?

It's the start of the 'overweight' range, which is a prompt to look at other measures, not a diagnosis.

Does BMI apply to children?

No – children use age- and sex-specific BMI percentiles.

⚖️Free BMI Calculator
Body mass index in metric or US units, with healthy range.Open tool →

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