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Child & Teen BMI Percentile Calculator

Unlike adult BMI, which uses fixed weight categories, children's BMI is assessed as a percentile relative to other children of the same age and sex. This calculator uses the CDC 2000 growth chart LMS method to convert your child's BMI into a percentile — giving you a more meaningful picture of their growth than a single number alone.

Quick Answer

A healthy BMI percentile for children ages 2–20 is between the 5th and 84th percentile for age and sex, based on CDC growth charts.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Enter age, sex, height, and weight to calculate the BMI percentile.

How the Formula Works

  1. Calculate BMI the standard way: divide weight in kilograms by height in meters squared.

    BMI = weight (kg) ÷ height (m)²

  2. Convert the child's age to months and look up the CDC LMS parameters (L, M, S) for that age and sex.

    Age in months = (years × 12) + additional months

  3. Calculate the z-score using the CDC Box-Cox power transformation.

    z = ((BMI / M)^L − 1) / (L × S)

  4. Convert the z-score to a percentile using the standard normal distribution.

    Percentile = Φ(z) × 100

Methodology & Sources

Reviewed and updated April 5, 2026 · Prepared by GetHealthyCalculators Editorial Team

This calculator uses the CDC 2000 LMS growth chart parameters for BMI-for-age in boys and girls aged 24–240 months. The Box-Cox power transformation converts raw BMI to a z-score, which is then mapped to a percentile via the standard normal distribution. Linear interpolation is used for ages between published data points.

References

How to Interpret Your Results

CDC weight status categories for children and teens are based on percentile rankings, not fixed BMI cutpoints. A percentile tells you how a child's BMI compares to other children of the same age and sex. For example, a child at the 60th percentile has a higher BMI than 60% of children the same age and sex.

Underweight
0–4.9 — Below the 5th percentile. Discuss growth patterns with a pediatrician.
Healthy Weight
5–84.9 — 5th to 84th percentile. Within the expected range for age and sex.
Overweight
85–94.9 — 85th to 94th percentile. A pediatrician can provide personalized guidance.
Obese
95–100 — 95th percentile or higher. Pediatric consultation is recommended.

Limitations

  • This tool uses simplified LMS lookup tables derived from CDC 2000 growth charts. Results are a close approximation — the official CDC BMI percentile calculator is the clinical standard.
  • BMI percentile is a screening tool, not a diagnostic test. It does not directly measure body fat or muscle mass.
  • Growth patterns vary among individuals. A single measurement is less informative than tracking percentiles over time.
  • This calculator covers ages 2–20. It is not designed for children under 2 years old or adults over 20.
  • Always discuss your child's growth, weight, and nutrition with a licensed pediatrician or registered dietitian before making health decisions.

Frequently Asked Questions

What is a BMI percentile and how is it different from adult BMI?
For adults, BMI categories (like "healthy weight" or "overweight") are based on fixed cutpoints that apply to everyone. For children and teens, the same cutpoints cannot be used because children's body composition changes significantly as they grow. A BMI percentile compares a child's BMI to other children of the same age and sex — a child at the 70th percentile has a higher BMI than 70% of same-age, same-sex peers.
What BMI percentile is considered healthy for a child?
According to the CDC, a BMI-for-age percentile between the 5th and 84th percentile is considered a healthy weight. Below the 5th percentile is underweight, the 85th to 94th percentile is overweight, and the 95th percentile or above is considered obese.
Why does the calculator ask for the child's sex?
Boys and girls have different growth patterns and body composition changes during puberty. The CDC growth charts use separate LMS parameter tables for boys and girls to accurately reflect these differences. Using the wrong sex category would produce an inaccurate percentile.
Is a high BMI percentile always a health concern?
Not necessarily. BMI percentile is a screening tool that flags children who may benefit from further evaluation — it does not diagnose any health condition. A child at the 88th percentile may be a healthy, muscular athlete. A pediatrician uses BMI percentile alongside other assessments (diet, activity, family history, physical exam) to determine if further evaluation or support is needed.
How accurate is this calculator compared to the official CDC tool?
This calculator uses LMS parameters from the CDC 2000 growth charts and the same Box-Cox z-score methodology used by the official CDC tool. Results should closely match the CDC's published tool. However, for clinical decisions, the CDC's official BMI percentile calculator or a healthcare provider's assessment should be used.
Can I use this calculator for a child under 2 years old?
No. This calculator covers ages 2 to 20 years, which matches the range of the CDC BMI-for-age growth charts. For children under 2 years, weight-for-length charts (rather than BMI) are the appropriate assessment tool, and those evaluations should always be done by a healthcare provider.
My child's percentile has changed between visits. Should I be concerned?
Some variation in BMI percentile is normal as children grow. A gradual, consistent upward trend — especially crossing major percentile thresholds — is more meaningful than a single number. Tracking percentile over time and reviewing those trends with your child's pediatrician is the best approach.

See how adult BMI is calculated and what the WHO categories mean

BMI Calculator

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