Child BMI Calculator: A Quick Tool to Monitor Growth

What This Tool Does

This calculator works out a child's BMI from age, gender, height, and weight, then shows where that BMI sits on a percentile bar relative to CDC-style growth chart bands for children of the same age and sex — not the fixed adult BMI categories.

Step-by-Step Instructions

1. Enter age (2–19) and select gender.
2. Choose metric (kg, cm) or imperial (lbs, ft/in).
3. Enter height and weight in the chosen units.
4. Click "Calculate BMI."

Worked Example

A 15-year-old girl who is 160 cm tall and weighs 50 kg has a BMI of 50 ÷ 1.60² = 50 ÷ 2.56 ≈ 19.5. This calculator's reference data for 15-year-old girls puts the 25th percentile at a BMI of 17.3 and the 50th at 19.9, so a BMI of 19.5 lands around the 46th percentile — a healthy weight for her age.

Reading the Output

You get a BMI number, a percentile, and a weight category (underweight, healthy weight, overweight, or obese), plus a color-coded bar chart showing where that percentile falls between the underweight, healthy, overweight, and obese bands.

Limitations

This calculator uses a simplified percentile table modeled on CDC growth chart guidelines, so treat the result as a close estimate rather than a clinical measurement. It is not a diagnosis — talk to a health professional for a full assessment, especially if a result is unexpected or a trend over time is a concern.

Common Use Cases

Parents doing a quick check between well-child visits, or caregivers watching a growth trend over several months rather than a single reading.