Child BMI Calculator
Calculate BMI for children aged 2-20 and show an approximate weight category. Note: clinical assessment requires age/sex-specific CDC or WHO growth charts.
Results
What is it?
DISCLAIMER: For educational and reference purposes only. All clinical decisions must be made by qualified healthcare professionals. BMI in children is calculated identically to adults (weight in kg divided by height in metres squared), but its interpretation is completely different. Unlike adult BMI, a child BMI value has no absolute meaning — it must be compared to age-and-sex-specific growth charts (CDC 2000 or WHO 2007 charts). Classification is by percentile: <5th = Underweight; 5th-84th = Healthy weight; 85th-94th = Overweight; >=95th = Obese. This calculator shows raw BMI only — it cannot determine percentile without reference to validated growth tables.
How to use
Enter weight in kg, height in cm, age in years, and sex. The calculator computes the raw BMI value and provides a very approximate categorical estimate for general reference. For clinical assessment, plot the BMI on the appropriate CDC or WHO growth chart for the child age and sex. The sex input is included for reference and future use.
Example scenario
An 8-year-old boy weighing 25 kg and 120 cm tall: BMI = 25 / (1.20)^2 = 17.4 kg/m². Using the CDC 2000 growth chart, a BMI of 17.4 at age 8 for boys corresponds to approximately the 75th percentile — healthy weight range. The raw BMI of 17.4 appears moderate but the percentile context is essential.
Pro tip
Always use the full growth chart for clinical paediatric assessment. A child with a BMI of 17 may be at the 50th percentile (healthy) at age 10 but at the 90th percentile (overweight) at age 6. Also assess growth velocity trends over time — a child whose BMI percentile has increased by more than 10 percentile points warrants investigation even if still within the healthy range. The American Academy of Pediatrics recommends annual BMI screening from age 2.