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If you're concerned about your child's growth, use this BMI percentile calculator for children and teens. If you don't know your child's BMI, this tool also has a build-in child BMI calculator. This information will help you to interpret pediatric growth chart (both BMI charts for teens and BMI charts for kids), so you can quickly find out if your baby's development is correct, and where among their peers they are placed. That's not all - in the article below, we explain how BMI classifications work and why is it essential to keep an eye on the kid's growth chart.

If this topic is interesting too you, feel free to take a look at our head circumference percentile calculator, which is handy in determining a child's rate of growth.

How to measure BMI?

BMI stands for Body Mass Index, which can be easily calculated with just body mass and height, just use the BMI formula:

BMI = body mass / height²,

Weight and height need to be in SI units (kilograms and metres respectively), as the BMI units are kg/m2. Remember that you can switch between the units directly in our BMI percentile calculator, or use any of our converters.

What is BMI classification?

Child BMI charts differ from adult BMI classifications. First of all, you don't read the BMI score directly, but have to interpret a special pediatric growth chart (or use our BMI percentile calculator) to know between which percentiles your child places.

This is because the BMI of a still growing prepubescent child may be unreliable - they tend to grow quickly, so their BMI becomes extremely inaccurate. On the contrary, during puberty, teens quickly gain weight, especially girls - and so their BMI increases. If a child is athletic, their BMI might be higher and potentially inaccurate, as muscles weigh more than fat.

Why is the child BMI chart useful?

Pediatric growth chart quickly reacts to any signs of developmental disorders. There are some thresholds which show that there's a need to react:

  • The child is at or above the 95th percentile, as they are considered obese.
  • The child is between the 85th and 94th percentile, as the child is overweight.
  • The child is below the 5th percentile, as the child is considered underweight. There are various possible reasons for child's low weight, among which may be loss of appetite, a growth spurt, or some more serious conditions, such as a consequence of the mother smoking during pregnancy.

In all these cases, calorie intake control may be useful.

The most crucial part of the day for a kid's proper growth is night. Due to the release of hormones, it's not only about adequate sleep length, but also about the time of going to bed. The largest pulses occur before midnight; therefore all children (including teenagers) should be asleep at that moment.

The BMI percentile calculator in practice

Let's explain how to use this kids growth chart calculation:

  1. First, give us some details:

    • age of your child - to one week (if less than 13 weeks old) or one month (if older).
    • whether they're a boy or a girl.
  2. Fill in the BMI of your child. You can also calculate his/her weight and height using the built-in BMI calculator for kids.

Get the results. The first number is the value of the kid's BMI, and the second which percentiles they fit into, with an explanation. There's also a graphic explaining where this percentile is with respect to other children.

In the next paragraph, you can read more about the interpretation of BMI classification.

How to interpret BMI chart for teens/kids?

Once you input all the information needed into this BMI calculator for kids, you'll see some numbers as a result. As mentioned above, the first is the exact percentile result. Just below that is the range in which your child places, e.g. between the 15th and 50th percentile.

A BMI percentile that is either below the 5th or above the 95th percentile should be concerning. In the first case, it might mean that your kid is too skinny for their height. In the second, they weight too much, and might need to lose some pounds. In both situations, we recommend that you consult a physician and a dietitian. Also, always check your kid's weight before any drug administration - as the dosage may differ depending on their body mass.

Otherwise, take a look at the information below.

Doctors consider the rate of growth as an important factor when looking at a pediatric growth chart:

  1. The child should follow the same percentile line on the chart as they grow.
  2. If the results cross two or more percentile lines (they raise/decrease by at least two ranges), e.g. from the 75th-85th percentile to the 15th-25th percentile, you should consult a doctor.
  3. Again, if their BMI is below the 5th or above the 95th percentile, check if the baby has always been in those ranges. If your child has only entered these ranges recently, consult a doctor. Also, a visit at a dietitian may be useful - as well as controlling their daily calorie intake.

Growth Chart WHO - an example

Growth Chart WHO (Arne Hendriks, CC BY 2.0, flickr.com)

Our data is derived from WHO (World Health Organization), and the standards were developed using data collected in the WHO Multicentre Growth Reference Study.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

Dominika Miszewska