Please read first
Children and teens need BMI-for-age percentile interpretation. This page can
calculate BMI from height and weight, but child BMI categories should be
based on age- and sex-specific growth charts. We do not show a percentile or
a weight category here, because doing so accurately requires official CDC
growth-chart data.
For the official percentile category, please use the
CDC Child and Teen BMI Calculator, and discuss the result with your
child's healthcare provider.
Why a child's BMI is read differently
Children and teens are still growing, and what counts as a healthy BMI
changes as they get older - and differs between boys and girls. Because of
that, professionals do not use the fixed adult bands (like 18.5-24.9) for
under-20s. Instead, a child's BMI is plotted on a growth chart to find a
BMI-for-age percentile. A percentile compares the child with others
of the same age and sex; for example, the 75th percentile means a higher BMI
than 75% of children in that group.
What this calculator does
Enter the child's height and weight (and age 2-19) and the tool returns the
BMI number using the standard formula - weight in kilograms divided by height
in metres squared, or the US equivalent. That is the same first step a
clinician uses. What we deliberately do not do is guess a
percentile or label the result, because an inaccurate category could be
misleading for a growing child.
Getting the official category
To turn the BMI number into a percentile category (such as underweight,
healthy weight, overweight, or obesity for the child's age and sex), use the
official CDC calculator linked below. It applies the proper growth-chart
reference data:
Open the CDC Child & Teen BMI Calculator
A note for parents and carers
A single BMI figure is not a verdict on a child's health, and it is not
something to worry about in isolation. Growth, development, activity, and
family history all matter. If you have any concerns about your child's
growth or weight, the best next step is a conversation with their paediatric
healthcare provider, who can interpret the percentile in context.
Frequently asked questions
Why is a child's BMI handled differently?
Children and teens are still growing, so a healthy BMI range changes with age and differs between boys and girls. Instead of fixed adult categories, child BMI is interpreted using BMI-for-age percentiles from growth charts. This page can calculate the BMI number, but the official percentile category should come from the CDC Child and Teen BMI Calculator.
Does BMI change by age?
For adults 20 and older, the BMI categories stay the same regardless of age - a BMI of 24 means the same thing at 25 as it does at 65. Age still matters for interpretation, because muscle and fat distribution change over time. For children and teens 2-19, BMI must be read against age- and sex-specific growth charts instead of adult categories.
What is a BMI calculator?
A BMI calculator is a simple tool that estimates your Body Mass Index from your height and weight. BMI is a screening measure used to place adults into broad weight categories. It does not measure body fat directly and does not diagnose any health condition - it is a starting point for a conversation with a healthcare provider.
Is my height and weight kept private?
Yes. The calculator runs entirely in your browser using JavaScript. Your height, weight, age, and any other input are never sent to a server or stored by us, so your measurements stay on your device.
How do you use this BMI calculator?
Choose US units or metric units with the toggle, enter your height and weight, optionally add age and sex for context, then select Calculate. Your BMI and adult category appear instantly. Nothing you type is sent anywhere - the calculation happens entirely in your browser.