Child & Teen BMI Calculator
Enter your child’s height and weight (metric or imperial) to work out their BMI. For children and teens, the number itself isn’t the whole story: BMI is read against age and sex on a growth chart to give a percentile, so use this as a starting point and let your child’s doctor interpret it.
Enter height and weight to calculate BMI.
Track the trend, not one number
A single BMI tells you little for a growing child. What helps is the pattern over time on an age- and sex-specific chart, which your doctor can plot.
General information only, not medical advice, and not a diagnosis. For children and teens, BMI must be interpreted by age and sex — discuss any concerns with your child’s doctor.
How it works
BMI is weight divided by height squared (kg/m², or 703 × lb/in²). It’s the same formula at any age, and this tool gives you that number.
The key difference for kids: adult BMI categories do NOT apply. A clinician plots the BMI on a CDC or WHO BMI-for-age chart to find the percentile for your child’s exact age and sex — that percentile, tracked over time, is what actually matters. A single number can look high or low and still be perfectly healthy for a growing child.
Frequently asked questions
How is BMI calculated? +
BMI = weight (kg) ÷ height (m)², or in imperial 703 × weight (lb) ÷ height (in)². This tool does the maths for you in either unit.
Can I use adult BMI categories for my child? +
No. Adult cut-offs (like 18.5–25 being normal) do not apply to children and teens. Their BMI must be read as a percentile for their age and sex — your doctor or a BMI-for-age chart does this.
What is a healthy BMI percentile for kids? +
Broadly, the 5th–85th percentile is often considered a healthy range, but it’s your child’s doctor who interprets it alongside growth history, build and overall health — not a single reading.
My child’s BMI looks high or low — should I worry? +
Not from one number. Children grow in spurts and body composition changes a lot. If you’re concerned, share the height, weight and dates with your doctor, who can plot the trend and advise.
Related reading
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