MasterTool

BMI Calculator for Kids

Calculate a child's BMI and BMI-for-age percentile using the CDC growth-chart LMS method for ages 2–20.

CDC BMI-for-age LMS parameters last updated · reference source

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Dated static reference; no live data is fetched. Verify current source values and assumptions before relying on results.

What this tool does

Calculate a child's BMI and BMI-for-age percentile using the CDC growth-chart LMS method for ages 2–20. CDC LMS parameters embedded from the official CDC bmiagerev.csv (ages 24–240 months, sampled at ≈6-month steps with linear interpolation — see src/data/health-tables.ts). Adult BMI bands must never be applied to children.

How to use the BMI Calculator for Kids

  1. Enter or select body weight in lb.
  2. Enter or select height in in.
  3. Enter or select age (months).
  4. Enter or select sex.
  5. Read the calculated result; change any measurement to compare alternatives.

Formula

BMI = kg/m²; z = ((BMI/M)^L − 1)/(L·S) using CDC BMI-for-age LMS parameters for the child's age and sex; percentile = Φ(z)
weight
Body weight (lb, before metric conversion)
height
Height (in, before metric conversion)
months
Age (months)
sex
Sex

CDC LMS parameters embedded from the official CDC bmiagerev.csv (ages 24–240 months, sampled at ≈6-month steps with linear interpolation — see src/data/health-tables.ts). Adult BMI bands must never be applied to children.

Worked example

For bmi calculator for kids, the following measurements illustrate the exact method: Body weight: 70; Height: 50; Age (months): 96; Sex: male.

Inputs

  • Body weight70 lb
  • Height50 in
  • Age (months)96
  • SexMale

Result

  • Child BMI19.69
  • BMI-for-age percentile94.11
  • BMI z-score1.56
  • CDC categoryOverweight (85th to below the 95th percentile)

Results explained

Child BMI
Child BMI from the formula above. CDC LMS parameters embedded from the official CDC bmiagerev.csv (ages 24–240 months, sampled at ≈6-month steps with linear interpolation — see src/data/health-tables.ts). Adult BMI bands must never be applied to children.
BMI-for-age percentile
BMI-for-age percentile from the formula above. CDC LMS parameters embedded from the official CDC bmiagerev.csv (ages 24–240 months, sampled at ≈6-month steps with linear interpolation — see src/data/health-tables.ts). Adult BMI bands must never be applied to children.
BMI z-score
BMI z-score from the formula above. CDC LMS parameters embedded from the official CDC bmiagerev.csv (ages 24–240 months, sampled at ≈6-month steps with linear interpolation — see src/data/health-tables.ts). Adult BMI bands must never be applied to children.
CDC category
CDC category from the formula above. CDC LMS parameters embedded from the official CDC bmiagerev.csv (ages 24–240 months, sampled at ≈6-month steps with linear interpolation — see src/data/health-tables.ts). Adult BMI bands must never be applied to children.

Frequently asked questions

Children's body composition changes as they grow, so a BMI is interpreted relative to children of the same age and sex. The percentile says what share of the CDC reference population has a lower BMI-for-age.

The CDC LMS method: published L, M and S parameters for each age and sex convert the BMI to a z-score, and the z-score to a percentile. The embedded table is sampled from the official CDC file at about 6-month steps and interpolated.

Below the 5th percentile is classed underweight, 5th to below the 85th is healthy weight, 85th to below the 95th is overweight, and the 95th or above is obesity.

24 to 240 months (2–20 years) — the range of the CDC BMI-for-age charts. For under-2s, growth is assessed with WHO standards and weight-for-length instead.

The LMS table is sampled at roughly 6-month steps and interpolated, and small measurement errors in height move BMI noticeably. Treat borderline results as approximate and confirm with your child's clinician, who also tracks the growth trend over time.