BMI Calculator for Teens

This BMI calculator for teens uses the CDC growth charts, not adult cutoffs. Enter a teen's age, sex, height and weight to see the BMI, the BMI-for-age percentile and the CDC category (underweight, healthy weight, overweight or obesity), plus the healthy weight range for that height. It is a screening result, not a diagnosis.

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Sex

Age: years

Age: extra months

Height (or feet if ft + in)

Height unit

Extra inches (feet + inches only)

Weight

Weight unit

How to use the BMI Calculator for Teens

Select boy or girl, because teen BMI is compared with the same sex.
Enter the teen's age in years and extra months. Ages 2 to 20 work, but this page is written for ages 10 to 19.
Enter height and weight in the units you have. For feet and inches, put feet in the height box and inches in the extra inches box.
Press Calculate. Read the percentile and category first, then the healthy weight band for that height.

Formula and method

Child and teen BMI uses the same arithmetic as adult BMI, BMI = weight (kg) / height (m)², but the number is then compared with the CDC reference distribution for the same sex and exact age instead of with fixed cutoffs. The CDC publishes three smoothing parameters for each age in months: L (skewness), M (median) and S (coefficient of variation). The calculator interpolates those values to the child's exact age, then computes the z-score z = ((BMI / M)^L − 1) / (L × S) (or ln(BMI / M) / S when L is 0). The percentile is the normal distribution function of z, multiplied by 100. A z-score of 0 is the 50th percentile; −1.64 is the 5th; +1.04 is the 85th; +1.64 is the 95th.

As a check, the CDC's own example of a 12-year-old girl who is 5 feet tall and weighs 136 pounds (BMI 26.6) lands at the 96th percentile with this method.

Healthy BMI range for teens by age

Age	Boys: healthy BMI (5th to below 85th)	Girls: healthy BMI (5th to below 85th)
10 years	14.2 to 19.4	14.0 to 19.9
11 years	14.5 to 20.2	14.4 to 20.8
12 years	15.0 to 21.0	14.8 to 21.7
13 years	15.4 to 21.8	15.3 to 22.5
14 years	16.0 to 22.6	15.8 to 23.3
15 years	16.5 to 23.4	16.3 to 24.0
16 years	17.1 to 24.2	16.8 to 24.6
17 years	17.7 to 24.9	17.2 to 25.2
18 years	18.2 to 25.6	17.5 to 25.7
19 years	18.7 to 26.3	17.8 to 26.1

These ranges are the 5th percentile up to below the 85th percentile from the CDC LMS tables. An adult BMI of 18.5 to 24.9 is not a valid shortcut for teens: the healthy upper limit changes with age and sex, as the table shows.

What percentile is a BMI of 22 at each age?

Age	Boy with BMI 22	Girl with BMI 22
12 years	89th	86th
13 years	85th	82th
14 years	81th	77th
15 years	75th	72th
16 years	68th	67th
17 years	60th	62th
18 years	51th	58th
19 years	43th	55th

A BMI of 22 sits in the healthy range for an adult, but for teens its meaning depends on age. The same number is high for a 12-year-old and ordinary for an 18-year-old, which is why teens need age-specific percentiles.

CDC BMI categories for teens

CDC category (ages 2 to 19)	BMI-for-age percentile
Underweight	Below the 5th percentile
Healthy weight	5th percentile to below the 85th
Overweight	85th percentile to below the 95th
Obesity, class 1	95th percentile up to below 120% of the 95th percentile
Obesity, class 2 (severe)	120% to below 140% of the 95th percentile, or BMI 35 to below 40
Obesity, class 3 (severe)	140% of the 95th percentile or more, or BMI 40 or more

How teen BMI is different from adult BMI

Adult BMI uses fixed thresholds. Teen BMI uses percentile curves that rise through adolescence because height and body composition keep changing. The calculator also reports a z-score, which tells you how many standard deviations the teen's BMI is from the median for the same age and sex. A z-score between about −1.6 and +1.0 corresponds to the healthy weight category.

Growth spurts and puberty timing

Teens do not all grow on the same schedule. Puberty can start earlier or later than average and growth spurts can briefly change BMI. A teen who is shorter for age but whose puberty has not started yet can show a different BMI percentile from a classmate of the same age. A pediatrician can place a single reading in context by looking at the growth curve over time.

Athletes and muscular teens

Muscle weighs more than fat for the same volume, so a teen who lifts weights or plays a strength sport can have a BMI above the 85th percentile while carrying little excess fat. If the reading does not fit what you see, ask a clinician about waist measurements, skinfolds or other measures before reading anything into the number. The Waist-to-Height Ratio Calculator is a simple second look.

Healthy habits matter more than the number

The BMI result is one input. U.S. physical activity guidelines recommend that young people ages 6 to 17 get at least 60 minutes of moderate-to-vigorous activity daily, and teens need roughly 8 to 10 hours of sleep. Regular meals, water, limited sugary drinks and time away from screens help most teens, whatever their percentile. Talk with a clinician before changing a teen's eating pattern.

Body image and eating concerns

Weight talk can be sensitive in the teen years. A BMI percentile should be treated as health information, not a judgement of the person. If a teen is skipping meals, restricting food, over-exercising, bingeing or very distressed about weight or shape, contact a doctor or a qualified mental health professional. In the United States the National Alliance for Eating Disorders helpline is a place to start.

When to see a doctor

See a pediatrician if the teen's BMI is below the 5th percentile or at or above the 85th, if their percentile has jumped across major lines, if weight change is rapid or unexplained, or if there are symptoms such as fatigue, excessive thirst, joint pain or snoring. A clinician can check growth history, puberty stage, blood pressure and labs where appropriate.

Frequently asked questions

What is a normal BMI for a 14-year-old?

There is no single number. For a 14-year-old boy the healthy range runs from about 16.0 to 22.6 and for a 14-year-old girl from about 15.8 to 23.3 (kg/m2), taken from the CDC 5th percentile up to below the 85th percentile.

Is a BMI of 18 underweight for a teen?

It depends on age and sex. A BMI of 18 is at about the 53rd percentile for a 12-year-old boy (49th for a girl), the 31st for a 14-year-old boy (30th for a girl) and the 13th for a 16-year-old boy (16th for a girl). Even at 17 it is still at about the 7th (boy) or 11th (girl) percentile, which is inside the healthy range, so a BMI of 18 is not underweight for most teens.

Can a teen use the adult BMI calculator?

No. Adult categories do not account for growth. Use age- and sex-specific percentiles as this page does.

Why does the percentile matter more than the BMI number?

Because the percentile tells you how the teen compares with others of the same age and sex, which is how the CDC defines the categories.

Does this tell me my teen's body fat?

No. BMI is a screening measure based on height and weight and does not measure body fat directly.

How often should teen BMI be checked?

Pediatricians usually track height and weight at routine visits, often yearly. The trend over visits matters more than any single reading.

Sources

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