Pediatric BMI Calculator (BMI-for-Age)

Q: Why can't I interpret a pediatric BMI like an adult BMI?

Children are still growing, so BMI changes with age and sex. Percentiles relative to age- and sex-matched CDC references are required for correct interpretation.

Q: When is pediatric BMI-for-age not appropriate?

BMI-for-age percentiles are not valid for children under 2 years of age, where weight-for-length charts should be used instead.

Calculates BMI for children and adolescents (ages 2–20) and classifies weight status using CDC 2000 BMI-for-age percentile references.

Pediatrics PediatricsEvidence-BasedUpdated 2026-08-09

Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.

Clinical Notes

Pediatric BMI is interpreted using age- and sex-specific CDC BMI-for-age percentiles (ages 2–20 years). Unlike adult BMI, a raw BMI value cannot be interpreted without knowing the child's age and sex.

Calculator Information

Specialty

Pediatrics

📋 Reference Ranges

Normal Range

5th to <85th percentile (Healthy weight)

Reference ranges for this calculator
Classification	Range
Underweight	< 5th percentile
Healthy weight	5th – <85th percentile
Overweight	85th – <95th percentile
Obesity	≥ 95th percentile

What This Calculator Measures

Calculates BMI for children and adolescents (ages 2–20) and classifies weight status using CDC 2000 BMI-for-age percentile references.

How to Use

Enter the child's age (2–20 years), sex, weight (kg), and height (cm).
Review the BMI and the BMI-for-age percentile.
Classify using the percentile: <5th underweight, 5th–<85th healthy, 85th–<95th overweight, ≥95th obesity.

How the Calculation Works

Pediatric BMI is calculated as weight in kilograms divided by the square of height in meters (BMI = weight (kg) / height (m)²). Since height is provided in centimeters, the calculator converts height to meters before squaring; the resulting BMI value is interpreted using age- and sex-specific percentile references.

Variables Explained

Age

Age in years used to select the appropriate age- and sex-specific BMI percentile reference.

Sex

Sex determines the age-specific percentile reference used to interpret BMI in children and adolescents.

Weight

Body weight in kilograms used in the BMI calculation.

Height

Height in centimeters, converted to meters and squared in the denominator for the BMI calculation.

Interpretation Guide

Pediatric BMI must be interpreted by age- and sex-specific percentiles, not raw BMI. Underweight <5th percentile; healthy weight 5th–<85th; overweight 85th–<95th; obesity ≥95th percentile.

Sex-specific interpretationAge-specific interpretationPediatric ranges differ

Clinical Significance

BMI-for-age percentiles are the standard screening tool for pediatric weight status, informing interventions for childhood obesity and its metabolic consequences.

When It Is Useful

Growth and weight assessment in children and adolescents aged 2–20 years
Screening for overweight, obesity, and underweight
Monitoring growth trajectory over time

When It Is Not Useful

In children under 2 years — use weight-for-length WHO charts
Without age and sex to reference percentiles
As a direct measure of body fat

Common Mistakes

Applying adult BMI weight-status cutoffs to an adolescent ignores that pediatric results are classified only by BMI-for-age percentile.
Calculating BMI-for-age for a child under 2 years uses the wrong reference, since weight-for-length WHO charts apply below that age.
Entering weight in pounds rather than kilograms produces an incorrect BMI and a misclassified percentile for the child.

Limitations

BMI does not distinguish fat from muscle mass.
Percentile references are population-based and may not apply to all ethnic groups.
Clinical assessment should include growth velocity, pubertal stage, and family history.

Worked Example

A 10-year-old boy weighs 35 kg and is 140 cm tall.

Inputs:

age: 10

sex: 1

weight: 35

height: 140

Expected Result: BMI = 35 / (1.40)² = 17.9 kg/m², at the 94.3rd percentile — Overweight (85th–<95th percentile).

Evidence & References

Source:: CDC Growth Charts
Reference:: Kuczmarski RJ, et al. Vital Health Stat 11. 2002;(246):1-190.

References

Kuczmarski RJ, Ogden CL, Guo SS, et al. 2000 CDC Growth Charts for the United States: Methods and Development. Vital Health Stat 11. 2002;(246):1-190. (Reference Standard)

Frequently Asked Questions

Why can't I interpret a pediatric BMI like an adult BMI?

Children are still growing, so BMI changes with age and sex. Percentiles relative to age- and sex-matched CDC references are required for correct interpretation.

When is pediatric BMI-for-age not appropriate?

BMI-for-age percentiles are not valid for children under 2 years of age, where weight-for-length charts should be used instead.

Which BMI Calculator Should I Use?

BMI

Adults with fixed BMI thresholds.

Not applicable to children.

Disclaimer: This calculator is intended for educational and clinical decision support purposes only. Pediatric weight assessment should also consider growth velocity, pubertal stage, and family history.

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