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Developed by the British Dietetic Association.


need to lose weight? BMI calculator

What's your Body Mass Index?

Your Body Mass Index (BMI) is a way of finding out if your weight is putting your health at risk and is used by health professionals around the world. It is based on your height and weight and can be worked out by taking your weight in kilograms and dividing it by your height (in metres) squared.

For any height there is a range of healthy weights. BMI is classified in the following way:

  • A BMI of less than 18.5 kg/m2 indicates you are underweight. You may need to gain weight.
  • If your BMI is 19 to 24.9 kg/m2, you're are a healthy weight, and should aim to stay that way.
  • A BMI of 25 to 29 kg/m2 is defined as overweight. It's a good idea to lose some weight for your health's sake, or at least aim to prevent further weight gain.
  • A BMI of over 30 kg/m2 is defined as obese and means your health is at risk. Losing weight will improve your health.

Note: BMI is not always a good reflection of body fatness. A very muscular person might have a high BMI when in fact their body fat is at a healthy level, as muscle weighs more than fat.

You should visit your GP if you feel you need help to manage your weight and health.

Body Mass Index