The detailed guide below is currently available in English.
Why children are not scored like adults
Body fat changes naturally as children grow, and it changes differently for boys and girls, so a single fixed healthy range would mislabel most of them. Pediatricians therefore plot BMI on BMI-for-age growth charts and read off a percentile: the 75th percentile means a child carries more relative mass than 75 of 100 peers of the same age and sex. Roughly, the 5th to 85th percentiles are considered healthy, 85th to 95th overweight, and at or above the 95th obese. The category this calculator shows applies adult cut-offs as a blunt approximation and is labeled accordingly.
Getting a usable number
Measure height without shoes against a wall and weight in light clothing, and record both to the nearest sensible unit. Track the trend over time rather than reacting to one reading: a child who jumps percentiles on the chart in either direction is the pattern pediatricians act on. Height and weight happen in spurts, so an unusually high or low single BMI often simply marks the week of a growth spurt. Any concerns belong with your child’s doctor, who can plot exact percentiles and interpret them alongside family history.
Repères pour la France
Repères locaux pour la France, utiles dans les calculs du quotidien :
- TVA: 20 % en taux normal (5,5 % alimentaire, 10 % restauration) ; les prix sont TTC par loi.
- Monnaie & paiements: Euro (€) ; paiement sans contact et carte bancaire très répandus, virement SEPA instantané en développement.
- Unités & nombres: Système métrique ; virgule décimale et espace pour les milliers : 1 234,56 €.
- Santé: Carte Vitale ; l'Assurance Maladie rembourse en base ≈ 70 % des soins, le reste par mutuelle.
- Pourboire: Service compris : aucun pourboire obligatoire ; arrondir suffit.
Mis à jour : octobre 2026 · valeurs 2025, sources officielles ci-dessus.
Questions fréquentes
Is my child’s BMI interpreted the same as an adult’s?
No. Children are assessed by percentile against CDC growth charts for their age and sex, so the adult labels shown here are only a rough orientation. A BMI of 17 might sit in the healthy range for a 10-year-old but underweight territory for a 17-year-old.
Where can I get the exact percentile?
Your pediatrician can plot the measurement on the official CDC BMI-for-age charts, and the CDC publishes downloadable chart PDFs. Bring the BMI number from this page along with age, sex, height, and weight to the appointment.
How is BMI calculated here?
The same formula as adults: weight in kilograms divided by height in meters squared. Pounds and inches are converted first (1 lb = 0.4536 kg, 1 in = 2.54 cm). Example: 35 kg at 140 cm gives 35 ÷ 1.96 = about 17.9.