The Body Mass Index (BMI) is a tool that can be used to tell how healthy a person's weight is. You can use the BMI to find out if you're a healthy weight for your height.

If you know your height and weight, you can work out which weight range you're in using the simple steps outlined below.

• Take your weight in kilograms (kg) and divide it by your height in metres (m).
• Then divide the result by your height in metres (m) again.

For example , if you weigh 70kg, and you're 1.75m tall, your BMI would be 22.9 (70/1.75 = 40 and 40/1.75 = 22.9).

BMI calculator

Alternatively, use our BMI calculator. Simply enter your height, weight and sex to find out your BMI. See the ' further information' section for a link to the BMI calculator.

The BMI weight ranges, as set out by the World Health Organization (WHO), are outlined below.

• If your BMI is less than 18.4 , you're underweight for your height.
  
• If your BMI is between 18.5 and 24.9 , you're an ideal weight for your height.
  
• If your BMI is between 25 and 29.9 , you're over the ideal weight for your height.
  
• If your BMI is between 30 and 39.9 , you're obese.
  
• If your BMI is over 40 , you're very obese.

If you have a BMI of over 25, you need to think about losing weight because you have an increased risk of developing serious health problems, such as heart disease, diabetes, and several forms of cancer.

If your BMI is over 30, you need to make some immediate changes to your lifestyle in order to lose weight.

Notes:

• This is general advice for adults only - it doesn't apply to children.
  
• When you work out your BMI, remember to take into account your body frame and your build - your BMI may not be accurate. For example, your BMI may not be accurate if you're a weight-trainer, an athlete, or if you're pregnant, or breastfeeding.
  
• Your BMI may not be accurate if you're over the age of 60. This is because your bones may begin to weigh less as you get older.
  
• If you have a long-term health condition, talk to your doctor before starting any weight-loss program.
  
• Talk to your doctor if you have noticeably lost, or gained, weight recently for no known reason.