BMI Percentile Calculator
Compute BMI and BMI percentile for children and teens (ages 2–20). Adult BMI cut-offs do not apply at these ages.
What is BMI Percentile?
BMI percentile is the gold-standard pediatric weight metric because absolute BMI numbers shift dramatically through childhood. A 12-year-old with BMI 22 may be obese, while a 19-year-old with the same BMI is healthy. Percentiles compare against same-age, same-sex peers and are categorised as: under 5th = underweight, 5–84th = healthy, 85–94th = overweight, 95th+ = obese.
How is it calculated?
BMI = weight (kg) / height (m)². The percentile uses an age-specific mean and SD approximation of the CDC growth-chart curves to compute a z-score, which is then converted to a percentile via the standard normal CDF.
Frequently Asked Questions
- Why are there separate cut-offs for children?
- Body composition changes rapidly through growth; absolute BMI thresholds would mis-classify most children.
- Should children diet?
- Weight-management plans for children must be supervised by a paediatrician.
- How is teen BMI measured?
- Same formula, but interpreted on the age- and sex-specific percentile chart.
- Are CDC and WHO charts the same?
- No — WHO is used 0–2 years; CDC for 2–20 in the United States.