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BMI Calculator for Teens

Health

Calculate BMI-for-age for teenagers aged 13-19 and see an estimated CDC growth-chart percentile with weight category. Fast, free, and mobile-friendly.

Sex
Age15yrs
1319
Height64in
4878
Weight125lbs
60300

BMI

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Note: This percentile is an approximation of the CDC BMI-for-age growth charts. For an official clinical percentile, ask your pediatrician to plot BMI on the CDC growth chart directly.

What is a Teen BMI?

A BMI Calculator for Teens estimates Body Mass Index for adolescents aged 13–19 and places that number in context using the CDC's BMI-for-age growth charts. Unlike the standard BMI Calculator, which applies fixed adult cut-offs of 18.5, 25, and 30, this tool compares a teenager's BMI against thousands of other teens of the same age and sex to produce a percentile — the same approach pediatricians use during well-child visits.

The reason age and sex matter so much during the teen years is puberty. Growth spurts, muscle development, and changes in body composition happen at different rates and different ages for boys and girls, so a BMI of 22 might be completely normal for a 17-year-old boy but elevated for a 13-year-old girl. The CDC growth charts, first published in 2000 and still the U.S. clinical standard, capture this variation by tracking BMI-for-age as a percentile curve rather than a single number line.

This calculator uses a close mathematical approximation of those CDC percentile curves. It is designed as a quick screening estimate for parents, students, and health-conscious teens — not a replacement for the exact clinical growth chart a pediatrician uses, which also tracks a teen's BMI trend across multiple visits over time.

How to use this Teen BMI calculator

  1. Select Sex — Boy or Girl — since CDC reference curves differ by sex.
  2. Set Age using the slider, from 13 to 19 years.
  3. Enter Height in inches using the slider or type an exact value.
  4. Enter Weight in pounds using the slider or type an exact value.
  5. The calculator instantly displays the BMI value, the estimated CDC percentile, and the weight category with a color-coded badge.
  6. Use the step-by-step breakdown below the result to see exactly how the BMI and percentile were derived.
  7. If the result falls outside the healthy 5th–85th percentile range, treat it as a prompt to discuss with a pediatrician rather than a final diagnosis.

Formula & Methodology

Step 1 — Calculate raw BMI (U.S. customary units):

BMI = 703 × weight (lbs) ÷ height (in)²

Step 2 — Estimate the percentile:

The calculator compares the raw BMI to an approximated median BMI value for the teen's exact age and sex, derived from published CDC BMI-for-age reference points. It computes a z-score using the formula z = ((BMI ÷ Median) − 1) ÷ S, where S is an age/sex-specific spread parameter, then converts that z-score to a percentile using the standard normal distribution.

Worked example:

A 15-year-old boy is 64 inches tall (5'4") and weighs 125 lbs.

1. BMI = 703 × 125 ÷ 64² = 87,875 ÷ 4,096 = 21.5
2. Compared to the median BMI for 15-year-old boys (~20.5), this places him modestly above the median.
3. Estimated percentile: roughly the 65th percentile — solidly within the Healthy weight band (5th–85th percentile).

Assumptions and limitations:

- This calculator uses a mathematical approximation of the CDC LMS growth-chart tables, not the exact published lookup values — treat the percentile as an estimate, not a clinical figure.
- BMI-for-age does not distinguish muscle from fat; athletic teens with high lean mass may show an elevated percentile without excess body fat.
- Results are for teens aged 13–19 only. For children under 13, use official CDC pediatric growth charts with a pediatrician. For adults 20 and over, use the standard BMI Calculator.

Frequently Asked Questions

BMI-for-age applies the same weight-to-height formula as adult BMI, but interprets the result differently. Instead of fixed cut-offs like 25 for overweight, a teen's BMI is compared against thousands of other teens of the same age and sex on a CDC growth chart, producing a percentile. This accounts for the rapid and uneven growth that happens during puberty, which fixed adult cut-offs do not capture.
The formula is identical to the adult version: BMI = 703 × weight (lbs) ÷ height (in)², or weight (kg) ÷ height (m)² in metric units. What changes is the interpretation step — the raw BMI number is then plotted against age- and sex-specific CDC reference data to find a percentile rather than compared to a flat category table.
According to the CDC, a BMI-for-age between the 5th and 85th percentile is considered a healthy weight for children and teens aged 2 to 19. Below the 5th percentile is classified as underweight, between the 85th and 95th percentile as overweight, and at or above the 95th percentile as obese.
Teens are still growing, and the proportion of muscle, bone, and fat to height changes constantly during puberty — differently for boys and girls and at different ages. The adult BMI Calculator uses static cut-offs (18.5, 25, 30) that assume growth has finished, which would misclassify a perfectly healthy 14-year-old. The teen version accounts for age and sex by comparing against a percentile curve instead.
No — this calculator provides a close mathematical approximation of the official CDC BMI-for-age growth charts, not the exact published lookup table. It is a useful screening estimate, but your pediatrician's office uses the precise CDC L/M/S tables and can plot your teen's BMI trend over multiple visits, which this single-point calculator cannot do.
Yes. Boys and girls follow different growth trajectories through puberty, so the CDC maintains separate reference charts and separate median BMI curves for each sex at every age from 2 to 19. This calculator applies sex-specific reference values before calculating the percentile, which is why selecting the correct sex matters for an accurate result.
A single BMI-for-age reading is a screening tool, not a diagnosis. If the result falls outside the 5th–85th percentile healthy range, discuss it with a pediatrician, who will consider growth history, family history, and physical development before recommending any changes to diet or activity.
Yes. A teen with a high amount of lean muscle mass — common in athletes — can show a BMI-for-age in the overweight range even though their body fat is low. In these cases, a body composition measurement like the Body Fat Calculator gives a more accurate picture than BMI-for-age alone.
CDC growth charts for BMI-for-age cover ages 2 through 19. Once a person turns 20, the standard adult BMI Calculator with fixed category cut-offs (underweight, normal, overweight, obese) becomes the appropriate tool.
Most pediatricians check BMI-for-age at annual well-child visits as part of routine growth monitoring. Checking more frequently than every few months is not usually necessary unless a doctor is actively monitoring a specific weight-related concern.
This calculator uses U.S. customary units — height in inches and weight in pounds — matching how pediatric growth is typically recorded in the United States. The same 703 × weight ÷ height² formula works internationally once height and weight are converted to feet/inches and pounds.
Not always. Because BMI does not distinguish between fat and muscle, a muscular or large-framed teen may fall into a higher percentile without excess body fat. Pediatricians typically combine BMI-for-age with a physical exam, growth history, and sometimes waist circumference before drawing conclusions about a teen's weight status.
Also known as
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