Body Mass Index (BMI) is a good way to check if you're a healthy weight. For adults, BMI is a measure of whether you're a healthy weight for your height.
For children aged two and over, BMI centile is used. This is a measure of whether the child is a healthy weight for their height, age and sex.
If you have a BMI above the healthy range you are at raised risk of the serious health problems linked to being overweight, such as type 2 diabetes, heart disease and certain cancers. In children, BMI centile indicates whether the child is a healthy weight.
Who can use BMI and BMI centile?
BMI is the best assessment of weight in adults, and BMI centile is the best assessment for children aged two and over.
Some adults who have a lot of muscle may have a BMI above the healthy range. For example, professional rugby players can have an 'obese' BMI result despite having very little body fat. However, this will not apply to most people.
BMI for adults
BMI takes into account that people come in different shapes and sizes. That's why a range of BMIs is considered healthy for an adult of any given height.
A BMI above the healthy range indicates that you're heavier than is healthy for your height.
The ranges below only apply to adults. BMI results are interpreted differently for children.
- BMI below 18.5: a score this low means that you may be underweight. There are a number of possible reasons for this. Your GP can help you find out more, and achieve a healthy weight.
- BMI between 18.5-24.9: this is a healthy range. It shows that you're a healthy weight for your height. However, it's still important to eat a healthy, balanced diet and include physical activity in your daily life if you want to maintain a healthy weight.
- BMI score of 25 or more: your BMI is above the ideal range and this score means you may be overweight. This means that you're heavier than is healthy for someone of your height. Excess weight can put you at increased risk of heart disease, stroke and type 2 diabetes. It’s time to take action.
- BMI of 30 or more: a BMI above 30 is classified as obese. Being obese puts you at a raised risk of health problems such as heart disease, stroke and type 2 diabetes. Losing weight will bring significant health improvements, and your GP can help
BMI for children
BMI results are interpreted differently for children.
When interpreting BMI for a child, health professionals look at a child's weight in relation to their height, age and sex. The result is called the child’s BMI centile. BMI centile is a good way of telling whether a child is a healthy weight, and is used by healthcare professionals.
Using your child’s BMI centile, a healthcare professional can tell whether they're growing as expected. You may have done something similar when your child was a baby, using the growth charts in the Personal Child Health Record.
Once your child’s BMI centile has been calculated, they will be in one of four categories:
- underweight: below 2nd BMI centile
- healthy weight: between the 2nd and 90th BMI centile
- overweight: between 91st and to 97th BMI centile
- obese: at or above 98th BMI centile. This BMI centile category is called 'very overweight' in letters that are sent by the National Child Measurement Programme.
Most children should fall in the healthy weight range. A BMI at or above the 91st centile is likely to indicate your child has an increased risk of obesity-related health problems.
Some medical conditions or treatments may mean that BMI centile is not the best way to measure whether your child is a healthy weight. Your GP or other health professional can discuss this with you.
If your child is overweight
Research shows that children who are overweight or obese have a higher risk of ill health during childhood and in later life. If your child is overweight, it’s time to take action.
A GP or practice nurse can give advice and support on helping your child achieve a healthy weight as they grow.
If you would like further information, please consult the 'helpful links' section on this page.
The more physical activity you do, the greater the benefit.