Child Teen BMI Calculator

Calculate BMI-for-age for children and teenagers using CDC growth-chart percentiles, then review category thresholds and a height-based healthy-weight range.

Units

Sex on growth chart

Result

54th percentile

BMI-for-age for a 10 years old boy using the CDC 2-to-20-year growth charts.

BMI
16.8
Category
Healthy weight
% of 95th percentile
76%
Healthy-weight range
27.05 kg to 36.86 kg
Healthy weight BMI-for-age is between the 5th and 85th percentiles on the CDC growth charts, which is the usual healthy-weight range for children and teenagers.

CDC thresholds used here

Healthy weight spans the 5th to under-85th percentiles. Obesity begins at the 95th percentile, and severe obesity starts at 120% of the 95th percentile or BMI 35 kg/m².

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Paediatric Growth

Child and teen BMI calculator guide: CDC percentiles, categories, and when to get help

A child and teen BMI calculator does not use the same fixed cutoffs as an adult BMI tool. For ages 2 to 19 years, BMI has to be interpreted against age- and sex-specific CDC growth-chart percentiles, because height, weight, and body composition change rapidly through childhood and adolescence.

Why adult BMI bands do not work for children

Adult BMI uses fixed category cutoffs because adult growth has stabilised. In children and teenagers, the same BMI value can mean something very different at age 4, 10, or 17, and the expected range also differs between boys and girls. That is why paediatric BMI is a screening measure based on BMI-for-age percentile, not a direct diagnosis.

The most useful question is not only “what is the BMI?” but “where does this BMI sit on the growth chart for this child’s age and sex?” A percentile result helps clinicians judge whether the measurement falls below, within, or above the usual range for peers.

How the CDC percentile method works

The calculator first converts the height and weight into BMI, then matches that BMI to the CDC 2-to-20-year reference data for the selected sex and exact age in months. It also reports the 5th, 85th, and 95th percentile thresholds and the percentage of the 95th percentile, which is useful when the result is above the obesity threshold.

For very high BMI values, the CDC program uses an extended approach above the 95th percentile instead of leaving every higher value flattened near the same top percentile. That gives a more informative result when a child or teen is well above the usual obesity cutoff.

BMI = weight (kg) / height (m)^2

Basic BMI is calculated first from height and weight.

% of 95th percentile = (child BMI / BMI at 95th percentile) x 100

Used to describe how far a BMI is above the standard obesity threshold.

Worked example

Suppose a 10-year-old girl measures 138 cm and 32 kg on the assessment date. Her BMI is about 16.8 kg/m². On the CDC growth charts, that sits around the middle of the healthy-weight range rather than near the underweight or overweight thresholds.

Now imagine a 13-year-old at the same height but a much higher weight. The BMI number alone still is not enough. The growth-chart comparison shows whether the result is above the 85th percentile, above the 95th percentile, or high enough to meet the severe-obesity definition based on 120% of the 95th percentile.

How to interpret the categories safely

CDC categories are underweight below the 5th percentile, healthy weight from the 5th percentile to below the 85th, overweight from the 85th to below the 95th, and obesity at or above the 95th percentile. Severe obesity is commonly described as 120% of the 95th percentile or a BMI of 35 kg/m² or higher.

Those labels still need context. Puberty stage, medical history, blood pressure, medications, family history, and the child’s growth trend over time can all matter more than a single measurement. Any underweight, obesity, or severe-obesity result should be reviewed with a paediatric healthcare professional rather than handled as a stand-alone conclusion.

  • This tool is for ages 2 to 19 years only.
  • A single BMI-for-age result is a screening flag, not a diagnosis.
  • Growth trend over time is often more important than one isolated value.
  • Children under 2 years need weight-for-length assessment instead of BMI-for-age.

Frequently asked questions

What age range is this calculator for?

It is designed for ages 2 years up to, but not including, 20 years. That matches the CDC child and teen growth-chart reference set. Children younger than 2 years are usually assessed with weight-for-length rather than BMI-for-age.

 Does a high percentile mean a child is unhealthy?

Not by itself. A high BMI-for-age percentile is a screening result that should be interpreted alongside growth trend, puberty stage, family history, blood pressure, diet, activity, and medical history. It tells you the child should be assessed in context, not that a diagnosis has already been made.

 Why does the calculator show percent of the 95th percentile?

Percent of the 95th percentile is useful when a BMI is already above the obesity cutoff. It helps describe how far above the threshold the result sits and is part of the CDC approach for higher BMI values, where plain percentile labels become less informative.

 Should I use this for sports-active or muscular teenagers?

Use it carefully. BMI still does not distinguish lean mass from fat mass, even in paediatric growth charts. Athletic teenagers can have a higher BMI because of muscle, so the result should be interpreted alongside body build, puberty, and clinical assessment.

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