Pediatric BMI Calculator

Pediatric BMI: WHO percentiles, ages 0–19

In children and teenagers, BMI is calculated the same way it is for adults, with BMI = weight(kg) / height(m)². What changes is how you read it. Instead of fixed thresholds, you look at where the value lands on percentile curves built for the child's age and sex. The references are the WHO Child Growth Standards for ages 0–5 and the WHO Growth Reference for ages 5–19. The bands run like this: P<5 is underweight, P5–P85 is a healthy weight, P85–P95 is overweight, and ≥P95 is obesity. Take a 7-year-old who weighs 25 kg at 1.20 m: that works out to a BMI near 17.4 kg/m², which sits around the 85th percentile. It's right at the edge of overweight, so it's worth keeping an eye on without panicking.

Applications

The Sociedade Brasileira de Pediatria (SBP) uses the WHO curves. The Caderneta da Criança from the Ministry of Health is the official booklet for tracking growth during puericultura (well-child care) at SUS. The BMI percentile fits into the ECA framework on a child's right to healthy development, and it's one of the metrics that show up in the Bolsa Família health conditionalities for kids up to 7 years old.

FAQ

Why not adult cut-offs (18.5 / 25 / 30)? A child's body composition shifts as they grow, so those thresholds would flag a perfectly healthy kid as underweight.

Is one measurement enough? No. Pediatrics follows the trajectory over several visits rather than a single reading. If a child crosses two percentile bands in either direction, that's worth looking into.

What if my child is at P90? That points to overweight risk. The pediatrician will weigh up diet, physical activity, sleep and family history before suggesting anything.

Does this replace the pediatrician? No. Treat it as a rough estimate. A real diagnosis also takes in Tanner stage, growth velocity and lab work.