How childhood BMI works
For children and teens, BMI is calculated the same way as for adults (kg ÷ m²) but interpreted very differently. A growing 8-year-old is supposed to have a much lower BMI than a 17-year-old, so a fixed table like 18.5–24.9 doesn't apply. Instead, paediatric BMI is compared against the CDC's growth charts to produce a percentile — for example, "75th percentile" means BMI is higher than 75% of children of the same age and sex.
CDC percentile bands
- Under 5th percentile — underweight
- 5th to 84th — healthy weight
- 85th to 94th — overweight
- 95th and above — obese
About this calculator
To keep the tool fast and offline, we use simplified age and sex-specific BMI cutoffs derived from the CDC growth charts. They're close to clinical values across most of the curve but should not replace a doctor's interpretation, especially when a child sits near a band boundary or has an unusual growth trajectory.
Helping a child reach a healthy weight
The best evidence for childhood weight is consistent, low-pressure habits: family meals, water instead of sugary drinks, plenty of sleep and unstructured outdoor play. Avoid restrictive diets for kids — they're linked to disordered eating in teens. Talk to a paediatrician before making big changes.