Child BMI Calculator
Estimate Child BMI values for health, wellness, and lifestyle planning.
This child BMI calculator finds a child's BMI and translates it into an age- and sex-specific percentile, using CDC growth chart standards - a more appropriate approach than the adult BMI categories, since children's healthy body composition changes significantly as they grow.
Enter your child's age, sex, height, and weight, and the calculator returns their BMI and percentile.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 8-year-old, 25 kg, 1.28 m | BMI ≈ 15.3 kg/m² | BMI = 25 ÷ (1.28 × 1.28) = 25 ÷ 1.638 ≈ 15.3. This value is then looked up against CDC growth chart data specific to 8-year-old boys or girls to find the percentile. |
| 10-year-old, 45 kg, 1.40 m | BMI ≈ 23.0 kg/m² | BMI = 45 ÷ (1.40 × 1.40) = 45 ÷ 1.96 ≈ 23.0 - notably higher than the first example, which would map to a higher percentile on the age- and sex-specific CDC chart. |
Why Children Use Percentiles, Not Fixed BMI Categories
Unlike adults, children's healthy body fat percentage naturally changes with age and differs between sexes as they grow, so a fixed BMI cutoff wouldn't be meaningful across all ages - percentiles instead compare a child's BMI to other children of the same age and sex from CDC growth chart reference data.
Reading BMI Percentile Categories
A BMI percentile below the 5th percentile is generally categorized as underweight, 5th to under the 85th as healthy weight, 85th to under the 95th as overweight, and 95th percentile or above as having obesity - these categories help track growth trends over time rather than serving as a single-point diagnosis.
How to Use the Child BMI Calculator
- Open the Child BMI Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the child bmi calculator works.
Frequently Asked Questions
How is BMI percentile different from adult BMI categories?
Adult BMI uses fixed numeric cutoffs, while child BMI is converted into a percentile relative to other children of the same age and sex, since healthy body composition changes significantly throughout childhood growth.
What BMI percentile is considered healthy for a child?
A percentile between the 5th and 85th is generally considered a healthy weight range under CDC growth chart standards, though a pediatrician should interpret any individual result.
Should I be concerned about a single BMI percentile reading?
A single reading is less informative than tracking the trend over time - pediatricians typically look at how a child's percentile changes across multiple growth visits rather than relying on one measurement alone.
How do I use this child bmi calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Child BMI Calculator calculate?
Estimate Child BMI values for health, wellness, and lifestyle planning. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this child bmi use?
The formula is: BMI = weight(kg) ÷ height(m)²; Percentile = rank against CDC age/sex growth chart. The CDC growth charts used for pediatric BMI percentiles were developed from a large nationally representative reference population and released in 2000, based on decades of survey data collected through the National Health and Nutrition Examination Survey (NHANES) - a large-scale, ongoing research program that has tracked American children's growth patterns since the 1960s.
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Last updated: September 27, 2026.