Reviewed by Arisa Tanaphon, Certified Tai Chi Instructor, Mindful Movement Specialist
Key takeaways
- This calculator is for adults aged 18 and over.
- BMI result categories are: underweight, a healthy weight, overweight, and obese.
- For some ethnic backgrounds, risk can increase at lower BMI values.
- BMI is one measure and does not directly separate muscle from body fat.
- If you are worried about your weight or health, contact a pharmacist or GP.
Who this calculator is for
Use this service to check the BMI of an adult aged 18 and over and get information about what to do next.
You should not use this tool to diagnose symptoms. If you are worried about your weight, speak to your local pharmacist or GP surgery.
Who should not use this tool
- are under 18 years old
- are pregnant
- have been diagnosed with an eating disorder, or think you may have one
- have a condition that affects your height
What you will need
- height
- weight
- ethnic background information
BMI Calculator (Adults 18+)
Calculate your body mass index and check your weight category.
Formula: BMI = weight(kg) / height(m)²
This calculator is for adults aged 18+ and is for guidance only.
For adults, BMI uses the same formula for female and male users.
Do not use this tool if you are pregnant, under 18, have (or may have) an eating disorder, or have a condition that affects height.
Your BMI result categories
- underweight
- a healthy weight
- overweight
- obese
How BMI is calculated
BMI is calculated as weight in kilograms divided by height in meters squared: BMI = kg/m².
The formula is simple and useful at population level, but it does not directly measure body fat percentage.
What your result means
A higher BMI is associated with increased risk of long-term conditions such as type 2 diabetes and heart disease.
However, BMI is only one measure of health. It cannot distinguish muscle from fat. For example, people with high muscle mass can be classified as overweight despite low body fat.
That is why waist measurement and clinical context can provide a better picture of overall health risk.
FAQ
References
Updated: 2026-04-15
