Child BMI Calculator

BMI (Body Mass Index) is calculated the same way for children as adults: weight (kg) / height² (m²). However, interpretation is completely different — instead of fixed thresholds (e.g., 25 = overweight), children use percentiles (centiles) that account for age and sex, because body proportions change during growth. The result should always be interpreted by a pediatrician.

A percentile is a child's position in a ranking of children of the same age and sex. For example, the 50th percentile means the child's BMI is higher than 50% of peers. The 85th percentile is the overweight threshold (only 15% of peers have a higher BMI), and the 95th is the obesity threshold. WHO and pediatricians use growth charts as the main assessment tool.

The calculator uses simplified thresholds based on WHO chart approximations: BMI < 14 is underweight, 14 to ~85th percentile is healthy weight, ~85–95th percentile is overweight, above the 95th percentile is obese. These are indicative values. Accurate assessment requires comparing with a full growth chart at a doctor's office.

Consult a pediatrician if your child's BMI falls in the underweight, overweight, or obese category, or if the child is rapidly gaining or losing weight, is inactive, complains of fatigue, or has breathing problems during sleep. The doctor will order tests and, if necessary, refer you to a dietitian or endocrinologist.

The calculator takes sex into account, but applies simplified percentile thresholds (WHO approximations). Full growth charts differ for girls and boys, especially during puberty (around ages 10–14), when body composition changes differently. For accurate assessment in this age range, a pediatrician consultation is recommended.

There is no single "healthy weight" — norms depend on height, sex, and age. A child growing along the same percentile (even if it is a low or high one) is usually healthy. Jumps between percentiles are concerning, e.g., from the 50th to the 90th in a year. Rather than a single measurement, what matters is monitoring the trend over time.

Yes — childhood obesity increases the risk of type 2 diabetes, high blood pressure, heart disease, orthopedic problems, and mental health issues (low self-esteem, depression). Over 70% of obese children remain obese into adulthood. Early intervention — dietary changes, physical activity, and psychological support — is far more effective than treatment in adulthood.

Do not introduce restrictive diets in children on your own — this can disrupt growth. WHO and pediatricians recommend: a varied diet rich in vegetables, fruits, and whole grains; limiting sugary drinks and fast food; at least 60 minutes of physical activity daily; limiting screen time. Always under the supervision of a doctor or pediatric dietitian.

The calculator covers children aged 2–18 years. For infants and children under 2, different indicators are used (weight-to-length ratio per WHO infant growth charts). For children over 18, standard adult BMI with thresholds 18.5 / 25 / 30 is used.

The calculator result is for informational and educational purposes. It uses simplified percentile models and does not replace a full clinical assessment by a pediatrician. If you have any concerns about your child's growth and weight, consult a specialist. Do not change your child's diet or activity level without advice from a doctor or certified pediatric dietitian.