Important Note : Teen BMI is a screening estimate, not a diagnosis. For children and teens, BMI should be interpreted by age and sex percentile, and results should be discussed with a healthcare provider when there are concerns.

Use this Teen BMI Calculator to estimate BMI, BMI Prime, CDC BMI-for-age percentile, and teen weight category from height, weight, age, and sex. It is designed for children and teens who need BMI interpreted by age and sex rather than by adult BMI cutoffs.

Reviewed by: AjaxCalculators Editorial Team
Last updated: April 26, 2026
Method source: CDC BMI formula, CDC BMI-for-age percentile guidance, and CDC child and teen BMI category cut-points
Editorial standards: AjaxCalculators Editorial Policy

What This Teen BMI Calculator Calculates

This calculator estimates:

• BMI in kg/m²
• BMI Prime
• CDC BMI-for-age percentile
• Teen BMI category

The calculator uses height, weight, age, and sex. Height can be entered in cm, m, or ft + in. Weight can be entered in kg or lb. Age and sex are needed because teen BMI results are interpreted using BMI-for-age percentiles, not only the raw BMI number.

Why Teen BMI Is Different From Adult BMI

Adults are usually grouped using fixed BMI ranges such as 18.5, 25, and 30. Teen BMI is different because children and teens are still growing. Their body fat patterns change with age, and the expected BMI range differs between boys and girls.

Because of that, a teen BMI result should be compared with other children and teens of the same age and sex. This comparison is called a BMI-for-age percentile.

How the Teen BMI Calculator Works

1) BMI Formula

BMI is calculated from body weight and height.

BMI = weight in kilograms ÷ height in meters²

If using U.S. customary units, the formula is:

BMI = weight in pounds ÷ height in inches² × 703

The calculator converts the entered height and weight into the correct measurement system before calculating BMI.

2) BMI Prime

BMI Prime compares the BMI value with the adult reference value of 25.

BMI Prime = BMI ÷ 25

For teens, BMI Prime can be useful as an extra ratio, but the more important interpretation is usually the CDC BMI-for-age percentile because age and sex matter during growth.

3) BMI-for-Age Percentile

For children and teens, BMI percentile shows how a teen’s BMI compares with the reference population of the same age and sex.

For example, a BMI at the 75th percentile means the BMI is the same as or higher than about 75% of teens of the same age and sex in the reference population.

4) Teen BMI Category

The calculator uses BMI-for-age percentile cut-points to estimate the teen weight category.

Assumptions and Important Notes

• This calculator is intended for children and teens in the CDC child/teen BMI age range.
• Age and sex are required for the BMI-for-age percentile result.
• BMI is a screening measure, not a medical diagnosis.
• The calculator does not directly measure body fat, muscle mass, bone mass, growth pattern, puberty stage, or overall health.
• Very athletic teens may have a higher BMI because of muscle mass.
• A teen with a low or high BMI percentile should not be judged by the number alone.
• For medical concerns, growth changes, eating concerns, or unexpected weight changes, discuss the result with a healthcare professional.

Worked Example

Suppose a 15-year-old teen has:

• Height: 165 cm
• Weight: 60 kg
• Age: 15 years
• Sex: selected in the calculator

Step 1: Convert height to meters
165 cm = 1.65 m

Step 2: Square the height
1.65 × 1.65 = 2.7225

Step 3: Calculate BMI
BMI = 60 ÷ 2.7225 ≈ 22.04 kg/m²

Step 4: Calculate BMI Prime
BMI Prime = 22.04 ÷ 25 ≈ 0.88

Step 5: Interpret by teen percentile
The calculator then compares the BMI value with CDC BMI-for-age reference data using the teen’s age and sex. That percentile is used to estimate the teen BMI category.

How to Use This Teen BMI Calculator

1. Enter the teen’s height.
2. Select the height unit: cm, m, or ft + in.
3. Enter the teen’s weight.
4. Select the weight unit: kg or lb.
5. Enter age.
6. Select sex.
7. Review the BMI, BMI Prime, percentile, and teen category results.

How to Interpret the Result

BMI shows weight relative to height. It is the starting value used for the calculation.

BMI Prime compares the BMI value with 25. For teens, it is only a supporting number and should not replace the BMI-for-age percentile.

Percentile shows where the teen’s BMI falls compared with other children or teens of the same age and sex.

Teen category gives a general screening category such as underweight, healthy weight, overweight, or obesity based on CDC-style percentile cut-points.

A single result should not be used to diagnose health. Trends over time, growth history, physical development, diet, activity, sleep, medical history, and professional evaluation all matter.

Practical Uses of a Teen BMI Calculator

• estimate BMI for a teen
• check BMI-for-age percentile
• understand whether adult BMI cutoffs are not appropriate for teens
• track general growth-related changes over time
• prepare questions for a doctor, pediatrician, dietitian, or school health provider
• compare height and weight in a quick educational screening tool

Common Mistakes to Avoid

• Do not interpret a teen’s BMI using adult BMI categories only.
• Do not ignore age and sex when reading a teen BMI result.
• Do not use BMI alone to judge fitness, appearance, or overall health.
• Do not treat one result as a diagnosis.
• Do not use inaccurate height or weight measurements, because small measurement errors can affect BMI and percentile results.
• Do not compare teens of different ages or sexes using only the raw BMI number.

References

1. AjaxCalculators live Teen BMI Calculator
2. CDC: Child and Teen BMI Calculator
3. CDC: Child and Teen BMI Categories
4. CDC Growth Chart Training: Calculating BMI
5. CDC: Extended BMI-for-Age Growth Charts Background

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• BMR Calculator
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Disclaimer: This calculator is for educational and screening use only. It does not diagnose underweight, overweight, obesity, eating disorders, growth problems, or any medical condition. For children and teens, BMI should be reviewed with age, sex, growth history, puberty stage, lifestyle, and clinical context. If you are concerned about a teen’s growth, weight, eating habits, body image, or health, speak with a qualified healthcare professional.