Child BMI Calculator

Enter your child's sex, age, height, and weight to calculate their BMI-for-age percentile. The Child BMI Calculator returns the BMI value, percentile rank, and weight category (Underweight, Healthy Weight, Overweight, or Obese) based on CDC growth charts for children and teens aged 2–19.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

Sex *

years

Enter age in whole years (2 to 19)

months

Additional months beyond the years entered

ft
in
cm
lbs
kg

Results

BMI

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BMI Percentile

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Weight Category

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Healthy BMI Range (Min)

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Healthy BMI Range (Max)

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Results Table

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Frequently Asked Questions

What is BMI-for-age and why is it different from adult BMI?

BMI-for-age compares a child's BMI to those of other children of the same age and sex using CDC growth charts. Unlike adults, where fixed BMI thresholds define categories, children's body fat naturally changes as they grow, so percentile rankings are used instead of absolute cut-off numbers.

What do the BMI percentile categories mean for children?

A percentile below 5 is considered Underweight, between 5 and below 85 is Healthy Weight, from 85 to below 95 is Overweight, and at or above 95 is classified as Obese. Severe Obesity is defined as a BMI at or above 120% of the 95th percentile or a BMI of 35 kg/m² or greater.

Is BMI an accurate measure of body fat for children?

BMI is a useful screening tool, not a diagnostic measure. It does not directly measure body fat and doesn't account for muscle mass, ethnic background, physical activity level, or puberty stage. A healthcare provider should assess the full picture of a child's health alongside their BMI result.

What age range does this Child BMI Calculator cover?

This calculator is designed for children and teens aged 2 through 19 years. For adults aged 20 and older, a standard Adult BMI Calculator using fixed thresholds should be used instead.

What should I do if my child's BMI percentile is too high or too low?

If your child falls outside the healthy weight range, speak with their pediatrician, family doctor, or a registered dietitian. Avoid putting children on restrictive diets without professional guidance. Focus on balanced nutrition, regular physical activity, and healthy routines.

Why does this calculator ask for the child's sex?

Boys and girls have different amounts of body fat and develop at different rates, especially during puberty. The CDC growth charts used to determine BMI percentile are sex-specific, so the child's sex is essential for an accurate percentile calculation.

How is BMI calculated for children?

BMI is calculated using the same formula as for adults: weight (kg) divided by height (m) squared, or [weight (lbs) × 703] divided by height (inches) squared. What differs is the interpretation — for children, the result is plotted against age- and sex-specific growth charts to determine a percentile.

Can I use this calculator for a child who is pregnant or has a growth disorder?

No. This calculator is not suitable for children who are pregnant, have been diagnosed with an eating disorder, or have a condition that affects their height or growth. In these cases, please consult a healthcare professional for a personalised assessment.