Free Online BMI Calculator
Calculate your Body Mass Index and understand your health better
Calculate Your BMI
Your result
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This is a screening estimate based on height and weight alone. BMI cannot tell you whether you are healthy: muscle mass, age and ethnicity all affect how it should be interpreted, and it is not suitable during pregnancy. If your BMI is outside the healthy range, or you have any concerns, speak with a healthcare professional.
BMI Categories (adults 18+)
A healthy weight means a BMI of 18.5 to under 25; a BMI of exactly 25 counts as overweight and exactly 30 as obese. Categories follow NHS adult guidance: NHS BMI health assessment tool.
Understanding Your BMI
Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = kg/m² where kg is a person's weight in kilograms and m² is their height in meters squared.
BMI is a screening tool that can indicate whether a person is underweight, healthy weight, overweight, or obese. However, BMI does not directly measure body fat, so some people, such as athletes, may have a BMI that identifies them as overweight even though they do not have excess body fat.
Why BMI Matters
BMI is used as a screening tool to identify potential weight problems in adults. It's a useful measure of overweight and obesity.
BMI Limitations
BMI doesn't account for muscle mass, bone density, or overall body composition. Athletes may have high BMI but low body fat.
Health Implications
A healthy weight is associated with a lower risk of conditions such as heart disease and type 2 diabetes.
Next Steps
If your BMI is outside the healthy range, consult with a healthcare provider for personalized advice and guidance.
BMI calculator questions
Is the BMI calculator free to use?
Yes. It is completely free, with no registration. You can calculate your BMI as many times as you like.
Is my data private?
Yes. All calculations run locally in your browser. Your height, weight and result are never sent anywhere or stored. See the Privacy Policy.
Can I trust the BMI result?
The calculator uses the standard adult BMI formula and NHS-style categories. BMI is still only a screening measure with known limitations — see About BMI.
Do you offer medical advice?
No. This site provides educational information and tools; it is not a substitute for professional medical advice, diagnosis or treatment.
Does it work on my phone?
Yes. The calculator is responsive and works on smartphones, tablets and desktop computers.