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What is BMI and What Do Your Results Mean?

The body mass index (BMI) is a way of working out if your weight is healthy by giving you a weight range for your height. Simply put, BMI is a calculation of your weight in kilograms divided by your height in metres squared.

BMI is not a perfect measurement and is best used in conjunction with other tests such as body fat percentage. For example, very muscular people, such as weight trainers and athletes, may be a healthy weight even though their BMI is classed as obese as muscle weighs much more than fat.

You should not use BMI as a measure if you are pregnant. Talk to your midwife or GP if you are concerned about your weight.

BMI is widely and consistently used, and unlike many other measurements, it works for both men and women without changing the calculation.

Calculate your BMI

What do your results mean

The ideal BMI for most adults is between 18.5 and 24.9*

If your BMI is:

  • below 18.5 – you're in the underweight range
  • between 18.5 and 24.9 – you're in the healthy weight range
  • between 25 and 29.9 – you're in the overweight range
  • between 30 and 39.9 – you're in the obese range

Underweight – less than 18.5

You may not be eating enough, or an illness could be preventing you from gaining weight. If you struggle to gain weight, see a GP.

Normal healthy weight – between 18.5 and 24.99

Adults in the normal range are considered to have a healthy weight. Maintain it with regular exercise and a healthy diet.

Overweight – between 25 and 29.99

A large percentage of adults in the UK fall into the overweight category. As mentioned before, there are factors that may cause your BMI to be inaccurate – for example if you have high muscle mass, it is therefore important to look at a range of measurements. If, however you do fall into this range, assess your lifestyle to see if you should reduce the number of calories in your diet or increase the calories you burn with exercise.

Obese – over 30

Being obese significantly increases your risk of developing a number of health conditions including heart disease and type 2 diabetes. If you are in this category you should see a GP and ask their advice on bringing down your weight.

*Figures shown vary based on ethnicity. Those shown are for the Caucasian European population. For South Asian ethnicity the 'normal' band is from 18.6 to 22.9, 'increased risk' is between 23 and 27.5 and 'obese' is 27.6 or above.