Teen & Child BMI (Percentile) Calculator
Work out a child or teenager’s BMI and see why it must be read against age- and sex-specific CDC percentiles, not adult cut-offs.
How it works
BMI = weight(kg) ÷ height(m)² · category = percentile of BMI on the CDC age- & sex-specific growth chart
Children and teens are still growing, so their body fatness changes with age and differs between boys and girls. A raw BMI number therefore cannot be judged against the fixed adult cut-offs (18.5 / 25 / 30). Instead the same BMI is converted to a percentile on the CDC BMI-for-age chart for that exact age and sex — the 85th and 95th percentiles mark overweight and obesity.
Worked example
A 12-year-old weighing 45 kg at 152 cm has a BMI of 45 ÷ 1.52² = 45 ÷ 2.31 = 19.5. Whether that is healthy depends on where 19.5 falls on the CDC chart for a 12-year-old boy — around the 75th percentile, which is still in the healthy 5th–85th band.
Sources: CDC — BMI for children and teens
Frequently asked questions
Why can’t I use the adult 18.5–25 range?
Adult cut-offs assume a fully grown body. A BMI of 19 is overweight for a 5-year-old but underweight for a 19-year-old, so children’s BMI is always interpreted as a percentile for their age and sex rather than against fixed numbers.
What percentile is “healthy weight”?
The CDC defines the 5th to 85th percentile as a healthy weight, 85th–95th as overweight and 95th or above as obesity, with below the 5th percentile classed as underweight.
Does this tool give the exact percentile?
It gives the BMI value; the percentile depends on detailed CDC growth reference tables. Plot the BMI on the official CDC BMI-for-age chart, or ask a paediatric provider, to read the precise percentile.
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Educational estimate only — not medical advice, diagnosis or treatment. Consult a qualified clinician for health decisions.