Child BMI Calculator

First: do not turn the number into a label

If you are checking your child's BMI, it is probably because something made you pause: a school note, a growth chart, a change in clothing size, food habits, screen time, sports, or a family history of diabetes or heart disease. That concern is understandable. The goal is not to make your child feel judged. The goal is to understand whether their growth pattern needs support, and what small family routines could help.

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.

What parents can look at before worrying

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

Small family changes beat big lectures

Children rarely respond well to weight lectures, and they should not be asked to manage an adult-sized health plan alone. Better changes are quiet and shared: water on the table more often, fruit within reach, fewer sugary drinks in the regular shop, a walk after dinner, earlier bedtime, active play that feels fun instead of corrective, and meals where nobody is mocked for appetite or body size. Your child is much more likely to feel safe when the whole household shifts the routine together.

Words that protect your kid's confidence

Try language like "your body is growing and we are checking the pattern" or "let's ask the doctor what this means." Avoid turning BMI into a nickname, a threat, or a daily score. A child who feels ashamed may hide food, avoid activity, or stop telling you how they feel. A child who feels supported is more likely to cooperate with small changes.

When to call your child's healthcare provider

Book a conversation if your child's BMI percentile changes quickly, if their eating or mood has changed, if they are being bullied about weight, if puberty seems early or delayed, if there are symptoms such as fatigue or excessive thirst, or if you simply feel unsure. A clinician can look at the growth chart, family history, development, blood pressure, and any tests that may be appropriate.