Child BMI Calculator
Calculate BMI and estimate BMI-for-age percentile for children and teens using age, sex, height, and weight.
Results
This calculator provides an estimated screening result only. Child BMI should be interpreted with official age- and sex-specific growth charts, growth history, puberty stage, health history, and a clinician’s judgment. It does not diagnose a medical condition.
Important Note : Child BMI differs from adult BMI. For children and teenagers, BMI is interpreted using age- and sex-specific percentile charts. A single BMI result cannot diagnose body fatness or a medical condition.
Use this Child BMI Calculator to estimate body mass index (BMI) and BMI-for-age percentile for children and teenagers. Unlike adult BMI, child BMI interpretation uses age and sex because children grow and develop at different rates.
Important: Child BMI results are screening tools and are not medical diagnoses. Growth pattern, development, and clinical assessment are also important.
Reviewed by: AjaxCalculators Editorial Team
Last updated: May 2026
Method source: CDC BMI-for-age percentile guidance
Editorial standards: Built using transparent formulas, interpretation tables, worked examples, and practical limitations.
What Is a Child BMI Calculator?
A Child BMI Calculator estimates a child’s Body Mass Index and then compares that value with age- and sex-specific growth references. Children and teens are still growing, so BMI is interpreted differently than adult BMI.
Healthcare providers commonly use BMI-for-age percentile charts when assessing growth patterns.
Child BMI Formula
The BMI equation itself remains:
BMI = Weight ÷ Height²
Metric:
BMI = kg ÷ m²
Imperial:
BMI = (lb ÷ in²) × 703
After BMI is calculated, the result is compared against age- and sex-based percentile reference charts.
Child BMI Category Reference
| Percentile | Category |
|---|---|
| Below 5th | Underweight |
| 5th–84th | Healthy Weight |
| 85th–94th | Overweight |
| 95th and above | Obesity |
Worked Example
| Input | Value |
|---|---|
| Sex | Boy |
| Age | 10 years |
| Height | 55 inches |
| Weight | 75 pounds |
BMI calculation:
(75 ÷ 55²) × 703
= 17.4 BMI
The calculator then compares that BMI with age- and sex-specific references and estimates a percentile category.
How to Use This Calculator
- Select child sex.
- Enter age.
- Enter height.
- Enter weight.
- Choose units.
- Click Calculate.
How to Interpret Results
| Result | Meaning |
|---|---|
| BMI | Height and weight ratio |
| Percentile | Comparison with children of same age and sex |
| Category | Weight status interpretation |
Common Mistakes
- Using adult BMI categories for children
- Entering incorrect units
- Interpreting one result without growth history
- Ignoring age or sex differences
Assumptions and Limitations
- Calculator assumes entered measurements are accurate.
- BMI does not directly measure body fat.
- Muscle mass and growth stage can influence interpretation.
- One result alone should not be used for diagnosis.
Practical Uses
- Growth tracking
- Health discussions with pediatricians
- Monitoring development over time
- Educational BMI estimation
References
- CDC BMI-for-age growth charts
- WHO Child Growth Standards
- American Academy of Pediatrics guidance
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Frequently Asked Questions
Is child BMI different from adult BMI?
Yes. Child BMI uses age and sex percentiles instead of fixed adult categories.
Can BMI diagnose obesity?
No. BMI is a screening tool and not a diagnosis.
Why does age matter?
Children grow rapidly, and BMI changes with age.
Why does sex matter?
Boys and girls develop differently during childhood and adolescence.
Can athletic children have higher BMI?
Yes. Muscle mass can affect BMI results.
Disclaimer : This Child BMI Calculator is intended for educational and screening purposes only. Child BMI is interpreted using age- and sex-specific percentiles rather than adult BMI ranges. A single BMI result does not diagnose overweight, obesity, underweight status, or any medical condition. Growth history, puberty stage, family pattern, physical activity, and clinical assessment should also be considered. Consult a qualified healthcare professional if you have concerns about a child’s growth or development.