Child BMI Calculator

For children and young people aged two to 18, the BMI calculator takes into account age and gender as well as height and weight.

Obese children are thought to be at increased risk of a variety of health conditions, and they’re also more likely to be overweight or obese as adults.

The BMI calculator works out if a child or young person is:

• underweight: on the 2nd centile or below. If you’re concerned about your child’s weight, see your GP. Find out more in underweight children
• healthy weight: between the 2nd and 91st centiles
• overweight: 91st centile or above. Get tips on how to encourage your child to be more active and eat well
• obese: 98th centile or above. If you’re concerned about your child’s weight, see your GP. Find out more in very overweight children

A child’s BMI is expressed as a “centile” to show how their BMI compares to children who took part in national surveys. For example, a girl on the 75th centile is heavier than 75 out of 100 other girls her age.

Measuring waist size is not routinely advised for children because it doesn’t take their height into account.

If you’re concerned about your child’s weight, contact your GP who may be able to refer you to your local healthy lifestyle programme for children, young people and families.

Limitations of the BMI

Your BMI can tell you if you’re carrying too much weight but it can’t tell if you’re carrying too much fat. The BMI can’t tell the difference between excess fat, muscle, or bone.

The adult BMI does not take into account age, gender or muscle mass. This means that: 

• very muscular adults and athletes may be classed “overweight” or “obese” even though their body fat is low   
• adults who lose muscle as they get older may fall in the “healthy weight” range even though they may be carrying excess fat

However, the BMI is a relatively straightforward and convenient method of assessing someone’s weight. 

Your can use your BMI result as a starting point for further discussion with your GP about your weight and your general health.

Find out more in How your GP can help and check out the Change4Life website for practical tips on staying healthy as a family.

If you’re suffering from an eating disorder, the BMI calculator results do not apply. Please seek further advice from your GP.

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