Child and Teen BMI Calculator guide
Child and Teen BMI Calculator: BMI Centiles Explained
Use our child and teen BMI calculator to work out a BMI centile for children and young people aged 2 to 19, and what it means for their weight.
By the AllCalculator editorial teamUpdated 16 October 20262 min read
Children's bodies change a lot as they grow, so the adult BMI categories don't apply to them. Instead, a child's BMI is compared with other children of the same age and sex. Our Child and Teen BMI Calculator does this for anyone aged 2 to 19.
How to use the calculator (Child and Teen BMI Calculator)
- Choose girl or boy.
- Enter your child's age in years and months.
- Enter their weight and height, in metric or imperial.
You'll see their BMI, their BMI centile, their weight category, and the healthy weight range for their current height.
What a BMI centile means
The centile shows how a child's BMI compares with others of the same age and sex. A child on the 50th centile is in the middle; a child on the 91st centile has a higher BMI than 91 out of every 100 children their age.
Weight categories for children
The calculator uses the cut-offs NHS clinicians use:
| BMI centile | Category |
|---|---|
| 2nd or below | Underweight |
| Above the 2nd to below the 91st | Healthy weight |
| 91st to below the 98th | Overweight |
| 98th or above | Very overweight |
Public health surveys, such as the National Child Measurement Programme, use the 85th and 95th centiles instead, so you may see different labels in different places.
A worked example
With the calculator's default settings, a 10-year-old girl who weighs 32kg and is 138cm tall has a BMI of 16.8. That's on about the 49th centile, a healthy weight. For her height, a healthy weight is roughly 25.8kg to 40.6kg.
The same BMI of 16.8 would mean something different for a 5-year-old or a 15-year-old, which is why age matters.
Where the data comes from
The centiles are calculated from the US CDC 2000 growth reference, a widely used and freely available standard. The NHS uses the UK 1990 reference, so the NHS calculator can give a slightly different centile, especially at the extremes. The overall picture is usually the same.
Supporting a healthy weight
- Focus on healthy habits for the whole family, not on weight or dieting.
- Aim for at least 60 minutes of physical activity a day for children and teenagers.
- Offer plenty of fruit and vegetables, and swap sugary drinks for water or milk.
- Make sure they get enough sleep.
Frequently asked questions
Should I put my child on a diet?
No, not without advice from a health professional. Growing children need enough energy and nutrients, and many children "grow into" their weight as they get taller.
Why does the healthy BMI change with age?
Children's body fat naturally changes as they grow. BMI usually falls after the toddler years, then rises again from around age 6.
At what age should I use the adult calculator?
From 18, use our BMI Calculator. For babies under 2, use our Baby Growth Calculator.
Sources and further reading
- NHS: Calculate BMI for children and teenagersnhs.uk
- NHS: Children's weightnhs.uk
- CDC: Growth chart data filescdc.gov
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This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.