BMI Calculator for Kids — BMI-for-Age Percentile (CDC 2000)
Unlike adult BMI, children's BMI must be interpreted relative to age and sex. Enter your child's sex, age, weight and height to get their BMI-for-age percentile using the CDC 2000 growth charts.
Sex
years
months
kg
cm
Body Mass Index for age — compare to the chart below
- 1
Height in metres
132 ÷ 100 = 1.32 - 2
Height squared
1.32² = 1.7424 - 3
BMI
32 ÷ 1.7424 = 18.4The percentile is then derived from the CDC 2000 LMS table for this age and sex.
How does this calculator work?
Children's BMI is interpreted as a percentile using the LMS method on CDC 2000 growth charts: BMI = W/H², then z = ((BMI/M)^L−1)/(L×S), then percentile = Φ(z). CDC categories: underweight <5th, healthy 5th–85th, overweight 85th–95th, obese ≥95th percentile — always age- and sex-specific.
Formula
How this is calculated
For children and adolescents (ages 2–20), the same BMI formula applies (weight in kg divided by height in metres squared), but the resulting number means something different at every age because children are still growing and their body composition changes. The CDC 2000 growth charts resolve this by expressing BMI as a percentile — that is, where the child's BMI falls relative to a large reference population of children of the same age and sex.
The LMS method (Box-Cox transformation) smoothes the skewed BMI distribution into a near-normal one at each age. The three parameters — L (power/skewness), M (median) and S (coefficient of variation) — are looked up from the published CDC 2000 tables, then a z-score is computed as z = ((BMI/M)^L − 1) / (L×S). Converting z to a cumulative normal probability gives the percentile. This calculator uses interpolated LMS values from the CDC 2000 tables.
The CDC defines weight categories for children as: underweight < 5th percentile; healthy weight 5th–84th; overweight 85th–94th; obese ≥ 95th. These cutoffs differ from WHO adult BMI ranges. Note that BMI-for-age is a screening tool, not a diagnostic one — body composition varies with puberty stage, muscle mass and ethnicity, and a healthcare provider should assess the full picture.
Frequently asked questions
Body fatness changes substantially as children grow, and the relationship between BMI and body fat differs between boys and girls. An adult BMI of 25 always means overweight; a child's BMI of 25 may be perfectly healthy at age 15 but overweight at age 10, because normal BMI values increase with age. Percentile charts account for this.
A single BMI measurement is a starting point, not a diagnosis. Consult your child's paediatrician, who will consider growth trends over time, pubertal stage, family history and diet. In most growing children the goal is to maintain weight while height increases, rather than to lose weight.
The CDC 2000 charts are based primarily on US data and are used internationally as a reference. Some countries (e.g., UK, India) use national charts. The WHO also publishes growth charts for ages 0–5 that are considered the global standard for young children.
TG we-Calculate Editorial Team. (2026). BMI Calculator for Kids — BMI-for-Age Percentile (CDC 2000) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/bmi-kids-calculator
TG we-Calculate Editorial Team. "BMI Calculator for Kids — BMI-for-Age Percentile (CDC 2000)." TG we-Calculate. 2026. https://we-calculate.com/calculator/bmi-kids-calculator.
TG we-Calculate Editorial Team, "BMI Calculator for Kids — BMI-for-Age Percentile (CDC 2000)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/bmi-kids-calculator
@misc{wecalculate_bmi_kids_calculator, title = {BMI Calculator for Kids — BMI-for-Age Percentile (CDC 2000)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/bmi-kids-calculator}}, year = {2026}, note = {TG we-Calculate} }
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