BMI Calculator for Kids & Teens

Children's BMI is not judged the same way as adults'. It is compared against growth percentiles for your child's age and sex.

This tool estimates BMI and an approximate percentile band. It is not a diagnosis — only a pediatrician can interpret a child's growth properly.

How kids' BMI is different from adult BMI

For adults, BMI is read against fixed cut-offs (under 18.5, 18.5–24.9, 25–29.9, 30+). For children and teens, the same BMI number means different things at different ages and for different sexes, because body composition changes rapidly during growth. Doctors therefore plot BMI on age-and-sex growth charts and read the percentile.

What the percentile bands mean

These bands follow the widely used CDC growth-chart definitions. A child in the 60th percentile, for example, has a BMI greater than 60% of children of the same age and sex.

How this calculator works

It first computes BMI the standard way — weight in kilograms divided by height in metres squared (kg ÷ m²). It then compares that number against reference growth data for the selected age and sex to estimate a percentile band. Growth data varies slightly between countries, so treat the result as a screening indication, not a verdict.

BMI alone cannot tell you whether a child is healthy: it does not measure body fat, muscle or growth trajectory. A pediatrician looks at the full growth curve over time, not a single reading.

When to see a doctor

• The result falls below the 5th or above the 85th percentile
• Your child's weight or height changes sharply between visits
• You have any concern about growth, appetite or activity

Related calculators

• Adult BMI calculator — fixed categories for ages 20+
• Calorie (TDEE) calculator — daily energy needs
• Water intake calculator — daily hydration

For general information only — not medical advice. Always consult a pediatrician.