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BMI Calculator for Adults

Body mass index (BMI) is a quick way to check whether your weight is in a healthy range for your height. This calculator is for adults aged 18 and over and uses the NHS and NICE weight bands.

Enter your height and weight to see your BMI.

BMI Ranges for Adults

  • Below 18.5: underweight
  • 18.5 to 24.9: healthy weight
  • 25 to 29.9: overweight
  • 30 to 39.9: obese
  • 40 or above: severely obese

For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, the NHS and NICE use lower thresholds: 23 to 27.4 for overweight and 27.5 or above for obese.

Limits of BMI

  • → BMI does not tell muscle from fat, so very muscular people may be classed as overweight.
  • → It is not suitable for children and teenagers, who need age- and sex-specific charts, or during pregnancy.
  • → For adults with a BMI under 35, waist-to-height ratio is a useful extra measure.
  • → If you are worried about your weight, speak to a GP or practice nurse.

Frequently Asked Questions

How is BMI calculated?

BMI is your weight in kilograms divided by the square of your height in metres (kg/m²).

What is a healthy BMI for adults?

For most adults a BMI of 18.5 to 24.9 is in the healthy range, 25 to 29.9 is overweight, 30 to 39.9 is obese and 40 or above is severely obese. For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, overweight starts at 23 and obesity at 27.5.

Is BMI accurate for everyone?

No. BMI does not tell muscle from fat, so muscular people can be classed as overweight. It is not used on its own in pregnancy, and children and teenagers need age- and sex-specific charts. For adults with a BMI under 35, measuring waist-to-height ratio adds useful information.

Estimate your daily calorie needs →

Sources

General information only, not a diagnosis. Last updated 2026-11-13.