bmicalculatorsystem.com
Enter your child's age, sex, height, and weight to get their BMI-for-age percentile and weight category — calculated with official CDC growth-chart data, instantly and privately.
Ages 2–20 · Free · Runs entirely in your browser
Supported range: 2–20 years (CDC charts).
Results update instantly. Nothing is stored or sent anywhere — all math runs in your browser using official CDC growth-chart data.
Result
16.8
kg/m²
58th
percentile
A 9-year-old boy with this BMI is in the healthy-weight range, higher than about 58% of children the same age and sex.
A child's BMI is a screening tool, not a diagnosis. Growth and body composition change rapidly in childhood — always discuss results with a pediatrician.
Why it's different
The BMI math is identical to the adult BMI calculator, but a single number means little for a growing child. Body fat naturally rises and falls with age and differs between boys and girls, so the CDC interprets a child's BMI as a percentile — how they compare to thousands of children of the same age and sex.
01
A BMI of 17 can be perfectly healthy at age 5 and underweight at age 15. Percentiles account for that automatically.
02
This tool uses the CDC 2000 growth-chart reference values (the LMS method) — the same standard pediatricians use in the United States.
03
Percentiles flag whether a closer look is worthwhile. Growth trends over time matter more than any single reading.
Classification
Children and teens aged 2–20 are classified by BMI-for-age percentile, not by the fixed adult cut-offs.
| Percentile range | Category |
|---|---|
| Below 5th percentile | Underweight |
| 5th to < 85th percentile | Healthy weight |
| 85th to < 95th percentile | Overweight |
| 95th percentile and above | Obesity |
For parents
If your child's BMI-for-age sits comfortably between the 5th and 85th percentile, that's the healthy range — keep supporting balanced meals, regular activity, and good sleep. If the result is below the 5th or at/above the 85th percentile, it's worth a conversation with your pediatrician rather than a cause for alarm.
Avoid putting children on restrictive diets without medical guidance. For most kids, healthy habits for the whole family — more vegetables and water, less sugary drinks and screen time, and active play — do more than any number on a chart. Track the trend across checkups; a single percentile is just one snapshot.
Want to check an adult instead? Use the main BMI calculator, or read more in our health blog.
FAQ
The BMI formula is the same as for adults — weight in kilograms divided by height in metres squared (kg/m²). What differs is interpretation: a child’s BMI is plotted against CDC growth charts to find a percentile for their exact age and sex, rather than compared to fixed adult cut-offs.
The CDC considers the 5th to below the 85th percentile a healthy weight. Below the 5th percentile is underweight, the 85th to below the 95th is overweight, and the 95th percentile or above is classified as obesity.
Children’s body composition changes constantly as they grow, and it differs by sex. A fixed BMI cut-off would be wrong at almost every age. Percentiles compare a child to a reference population of the same age and sex, which is far more meaningful.
It uses the CDC BMI-for-age charts, which apply to children and teens aged 2 through 20 years. For children under 2, the WHO growth standards are used instead — speak with your pediatrician.
No. BMI-for-age is a screening tool. A high or low percentile is a prompt to talk to a pediatrician, who can consider growth history, development, diet, and activity before drawing any conclusion.
The adult calculator gives your category, healthy weight range, and BMI Prime in seconds.
Open the adult BMI calculator