BMI healthy weight calculator

A good way to check if you're a healthy weight is to use the Body Mass Index (BMI). Your BMI is a measure of whether you're a healthy weight for your height.

It can indicate whether you're at raised risk of the serious health problems that are linked to being overweight, such as type 2 diabetes, heart disease and certain cancers.

Below is some information on how the calculation is performed by the NHS Choices BMI healthy weight calculator, as well as details of who to contact if you have concerns about you or your child’s BMI.

Information on calculation

To understand the results, it helps to know how they are calculated.

Adult results

For adults, the body mass index (BMI) is used to calculate whether a person is underweight, a healthy weight, overweight or obese for their height. BMI allows for natural variations in body shape, giving a healthy weight range for a particular height. The calculation divides the adult's weight in kilograms by their height in metres squared.

Child results

For children, BMI is used differently, as the child's age and sex have to be taken into account. To do this, a child growth chart is used to convert the 'BMI' into a 'BMI centile'. The BMI centile can be used to determine whether a child's BMI is within the healthy range or not.

Note: There are a number of growth references available for this purpose. This calculator uses the British 1990 Growth Reference for children aged four and over, and the WHO Growth Standards for children younger than four years.

The National Child Measurement Programme

As part of the National Child Measurement Programme, your child will be measured at school. Following this, you may receive a letter with your child's height, weight and BMI result. The letter may show the height and weight in both metric (i.e. centimetres and kilograms) and imperial (feet and inches and stones and pounds) units.

Please be aware that the imperial measurements on the letter may have been rounded up or down. Therefore, if you enter your child's height and weight as shown on the letter, you will need to input the metric measurements as these are more precise. Alternatively, you might want to measure your child yourself.

This calculator uses the clinical categories: "underweight", "healthy weight", "overweight" or "obese". Obese is a medical term used by doctors and health professionals. If you have received your child's results from the National Child Measurement Programme, you may notice that the term "very overweight" was used instead of "obese", but the results were calculated in the same way.

Need to speak to someone?

Any concerns about weight or growth should be discussed with a health worker.

You can speak to your:

    Health visitor (if the child is under 5 years old)
    School nurse (if the child is over 5 years old)
    GP or practice nurse