For educational purposes only. Not personalised health advice. This calculator has not been reviewed by a registered dietitian, physician or exercise physiologist. Results are population estimates and can be wrong for you individually. Speak to a qualified professional before acting on them, particularly if you are pregnant, under 18, managing a medical condition, or have a history of disordered eating.
Child and Teen BMI Percentile Calculator
For children and teenagers, body mass index is not read against fixed cut-offs the way it is for adults: the same BMI can be healthy at one age and high at another, and it differs between boys and girls. This calculator computes BMI from weight and height, then places it on the CDC BMI-for-age growth reference for ages 2 to 20, returning the BMI-for-age percentile and the CDC weight-status category. The percentile is the exact value from the CDC LMS parameters (the same method the CDC growth charts use), not an approximation. For example, a 10-year-old boy who weighs 32 kg and is 140 cm tall has a BMI of 16.33, which is the 44th percentile for his age and sex, a healthy weight. Enter your values below and the result updates instantly; you can also share a permalink that pre-fills the exact calculation. This tool is general information and is not a substitute for professional medical advice: only a clinician can assess a child's growth and health.
A Boy aged 10 years weighing 32 kg at 140 cm has a BMI of 16.33, the 44th percentile (Healthy weight).
Applies to: children and teenagers aged 2 to 20 years. Reference: CDC BMI-for-age LMS data, checked 2026-07-02.
The formula
BMI = weight (kg) / height (m)^2
BMI-for-age percentile (CDC LMS method): Z = ((BMI / M)^L - 1) / (L * S), or ln(BMI / M) / S when L = 0
Percentile = 100 * standard-normal-CDF(Z)
L, M and S are the CDC BMI-for-age values for the child's sex and exact age in months (L is the Box-Cox power, M is the median BMI, S is the coefficient of variation). Values between the tabulated ages are linearly interpolated, exactly as the CDC method specifies.
Worked example
With sex = Boy, age = 10 years (120 months), weight = 32 kg, height = 140 cm:
- Convert height to metres: 140 cm = 1.40 m
- BMI = 32 / (1.40 x 1.40) = 16.33
- CDC BMI-for-age parameters for a boy at 120 months: L = -2.7737, M = 16.62, S = 0.11979
- Z = ((16.33 / 16.62)^(-2.7737) - 1) / (-2.7737 x 0.11979) = -0.15
- Percentile = 100 x standard-normal-CDF(-0.15) = 44th percentile
- Weight status = Healthy weight (5th to under 85th percentile)
This worked example is a golden-value check verified against the CDC BMI-for-age data before this calculator was published.
CDC weight-status categories
- Underweight: below the 5th percentile
- Healthy weight: 5th to under the 85th percentile
- Overweight: 85th to under the 95th percentile
- Obese: 95th percentile and above
What this assumes
- Inputs are real numbers in the units shown, and age is between 2 and 20 years (the range of the CDC BMI-for-age reference).
- The percentile is computed from the CDC LMS parameters and reproduces the CDC smoothed percentile curves; it is a population reference, not a diagnosis. Only a clinician can assess a child's growth and health.
Frequently asked questions
Why use a percentile instead of a fixed BMI cut-off?
A child's healthy BMI range changes with age and differs by sex, so a single number cannot classify children the way the 18.5 to 25 adult range does. The CDC BMI-for-age percentile compares a child's BMI with a reference population of the same sex and age, which is why clinicians use it for children and teens aged 2 to 20.
Which reference does this use?
The 2000 CDC BMI-for-age growth reference (the published LMS parameters). The percentile is computed with the CDC LMS method and matches the CDC smoothed percentile curves exactly.
Does the result change over time?
The reference table is fixed, so the same inputs always give the same percentile. A child's own percentile can change as they grow, which is why repeated measurements over time are more informative than a single reading.
Official sources and verification
- CDC: Growth charts, the clinical growth-chart program.
- CDC: Percentile data files, the BMI-for-age LMS parameters embedded in this tool.
- CDC: Child and Teen BMI, weight-status category definitions.
This content is provided for educational purposes only and has not been reviewed by a qualified specialist in this field. See our methodology. General information, not professional medical advice.