Free BMI calculator for children and teens aged 2–19 — BMI, percentile and WHO weight category for age and sex, in kg/cm or lb/in.
Why children need a different BMI calculator
Children’s body fat changes a lot as they grow, and differs between boys and girls, so an adult BMI of 22 means something different for an 8-year-old. For children, BMI is compared with others of the same age and sex as a percentile or z-score. This calculator uses the WHO Child Growth Standards (2–5 years) and the WHO Growth Reference 2007 (5–19 years).
Age
Category (WHO)
BMI-for-age
5–19 years
Thinness
below −2 SD (about 2nd percentile)
5–19 years
Overweight
above +1 SD (about 85th percentile)
5–19 years
Obesity
above +2 SD (about 98th percentile)
2–5 years
Wasted
below −2 SD
2–5 years
Overweight
above +2 SD
2–5 years
Obese
above +3 SD
Doctors in the USA use the CDC growth charts, where 85th–94th percentile is “overweight” and 95th and above is “obesity” — results are usually similar. A single BMI is a screening number; your paediatrician looks at growth over time. Children should not be put on weight-loss diets without medical advice — see the kids diet chart for healthy meals.
Frequently asked questions
What is a healthy BMI percentile for a child?
Roughly between the 3rd and 85th percentile for age and sex using WHO references (5th–85th on CDC charts).
My child’s BMI is high — should they diet?
No. Talk to your paediatrician. The usual approach is healthy family meals, less sugary drinks and screen time, and more activity, so that the child grows into their weight.
Can I use the adult BMI calculator for teenagers?
Not until about 19–20 years. Teens should use BMI-for-age percentiles.