Calculator
BMI Calculator for Children
Calculate BMI for a child or teenager while clearly explaining that pediatric interpretation requires age- and sex-specific BMI-for-age references.
Calculate BMI for ages 2–19
Result
Why pediatric BMI is different
The BMI equation is the same mathematical ratio used for adults: weight in kilograms divided by height in metres squared. The crucial difference is interpretation. Children and teenagers are growing, so a BMI number must be compared with children of the same sex and age using a validated BMI-for-age reference.
What this calculator does — and does not do
This tool calculates the raw BMI for ages 2 through 19. It deliberately stops there. Without a validated pediatric reference dataset, it would be misleading to invent a percentile or category. The result therefore says "calculated BMI" and explains what additional information is needed for interpretation.
How pediatric interpretation works
In the CDC framework, BMI-for-age percentiles are used for children and teens. The reference categories include underweight below the 5th percentile, healthy weight from the 5th to below the 85th percentile, overweight from the 85th to below the 95th percentile, and obesity at or above the 95th percentile. Those categories depend on age and sex; they are not adult cutoffs applied to smaller bodies.
Worked example
A hypothetical 10-year-old who weighs 35 kg and is 1.40 m tall has BMI = 35 ÷ 1.40² ≈ 17.9 kg/m². That number alone does not tell us the pediatric category. To interpret it, the child's exact age, sex, and the selected reference standard are needed.
Growth, puberty, and trends
Growth is dynamic. A single measurement may be less informative than a pattern over time, particularly when a child is growing rapidly. Clinical interpretation may also consider height, weight trajectory, development, family history, nutrition, activity, and other health information.
Limitations
- No pediatric percentile is fabricated by this tool.
- Different reference systems can produce different percentiles.
- Raw BMI should not be compared with adult category cutoffs.
- This calculator is educational and does not replace pediatric clinical assessment.
Frequently asked questions
Can I use adult BMI categories for children?
No. Children and teens require BMI-for-age interpretation using age- and sex-specific reference data.
What ages are covered by pediatric BMI references?
The CDC child and teen BMI framework covers ages 2 through 19.
Why is sex needed?
BMI-for-age reference curves are sex-specific.
Why isn't a percentile shown here?
A valid percentile requires a specific reference dataset. This site does not invent one.
What does a 75th percentile mean?
It means the BMI is at or above the BMI of roughly 75% of the reference population of the same age and sex, subject to the details of the reference method.
Can a child's BMI change during puberty?
Yes. Growth and body composition change throughout childhood and adolescence.
Should parents use BMI alone?
No. Growth pattern and broader clinical context matter.
What about children under 2?
Adult BMI categories are not appropriate; infant growth is assessed using different measures.