BMI Percentile Calculator for Children and Teens (CDC)

1. Pick the sex and units. CDC growth charts are separate for boys and girls. Choose metric (kg, cm) or imperial (lb, in).
2. Enter the age. Type whole years, then any extra months. A 10-year-old who is 6 months older is 10 years and 6 months. The tool covers ages 2 to 19.
3. Enter weight and height. Use the units you picked. The tool computes BMI, then its percentile and z-score against the CDC data for that exact sex and age.

For adults, BMI is read against fixed cut points. For children and teens it is not, because healthy body fatness changes a lot with age and differs between boys and girls. The CDC instead ranks a child BMI against other children of the same sex and age.

That rank is the BMI-for-age percentile. A boy at the 72nd percentile has a BMI higher than about 72 percent of boys his age in the CDC reference population. The 50th percentile is the median.

The percentiles come from the CDC 2000 growth charts, built from national survey data. They apply to ages 2 to 19. Under age 2, clinicians use the WHO weight-for-length chart instead. Our guide to BMI for children and teens explains why the method differs from the adult one.

A percentile describes one measurement on one day. A pediatrician reads it alongside the growth trend over time, which matters more than any single point.

The tool first computes BMI, then applies the CDC LMS method to turn it into a z-score and a percentile.

1. BMI. Imperial inputs are converted first: 1 lb = 0.45359237 kg and 1 inch = 2.54 cm.
2. Look up L, M and S. The CDC publishes three numbers for each sex and age in months: L (a skew parameter), M (the median BMI) and S (a spread parameter). The tool holds the full CDC table and reads the row for the child sex and age, interpolating between the half-month rows for an exact age.
3. Z-score. The LMS formula above converts BMI into standard-deviation units. The CDC SAS program states it as z = ((BMI/M)^L - 1) / (L x S).
4. Percentile. The z-score is turned into a percentile with the standard normal distribution, the same probnorm step the CDC program uses. A z-score of 1.645 is the 95th percentile.

The normal CDF uses the Zelen and Severo approximation, whose error is under 0.000001 of a percentile, so it matches the exact value to several decimals.

Take a boy aged 120.5 months (10 years and about 2 weeks) with a BMI of 18.0 kg/m2.

1. The CDC row for a boy at 120.5 months is L = -2.765648008, M = 16.64613844, S = 0.120112464.
2. z = ((18.0 / 16.64613844)^-2.765648008 - 1) / (-2.765648008 x 0.120112464) = 0.58542.
3. percentile = normal CDF(0.58542) x 100 = 72.09, which the tool shows as 72.1.

A 72nd percentile falls between the 5th and 85th, so the CDC category is healthy weight. As a cross-check, the same CDC row lists the median BMI (50th percentile) as 16.65 and the 85th as 19.39, and a BMI of 18.0 sits between them, consistent with the 72nd percentile.

CDC Percentile Curves for That Row

These BMI values are read straight from the CDC BMI-for-age data file for that row.

The CDC groups BMI-for-age percentiles into four weight-status categories. The wording below is the CDC wording.

The tool colours the result green for a healthy weight, amber for underweight or overweight, and red for obesity. The colour is a screening signal, not a diagnosis.

A Note on Severe Obesity

The CDC also describes severe obesity as a BMI at or above 120 percent of the 95th percentile, or a BMI of 35 kg/m2 or higher. That uses the separate CDC extended BMI-for-age charts, which are not part of the standard percentile table this tool uses, so the tool does not label it.

The arithmetic is exact, but the percentile it produces depends on the measurements and on the child.

Measurement Accuracy

Small errors in height change BMI more than weight does, because height is squared. Measure without shoes and record height carefully.

Age in Months

Because BMI changes fast in childhood, the tool uses age in months, not just years. A child who is a few months older can land on a different percentile.

Body Build

BMI does not separate muscle from fat. A very muscular teen can sit at a high percentile without excess fat, which is one reason a percentile is a screen, not a diagnosis.

The Reference Population

Percentiles compare a child to the CDC 2000 reference children. They describe rank in that group, not an ideal.

Growth Trend

One point says little on its own. A pediatrician looks at whether the percentile is steady, rising or falling across visits.

The two methods answer different questions, so the numbers are not interchangeable.

For anyone aged 20 or over, use the adult BMI calculator instead. For more on what BMI can and cannot say about health, see how BMI relates to health risk.

Checking a Routine Measurement

After a height and weight at home or at school, a percentile shows where a child sits for their sex and age.

Understanding a Clinic Result

If a visit mentioned a percentile, this tool reproduces the CDC method so you can see how it is reached.

Converting Units

It reads both metric and imperial, so a measurement in pounds and inches gives the same percentile as kilograms and centimetres.

Teaching the Method

The step-by-step z-score and percentile make it a clear example of the LMS method behind growth charts.

1. Using Adult Cut Points on a Child

A BMI of 24 is in the adult healthy range but can be a high percentile for a young child. Always use the age-and-sex percentile for under-20s.

2. Entering Age in Years Only

Dropping the extra months can shift the percentile. Enter the months too.

3. Mixing Units

Entering pounds while the tool is set to metric gives a wrong BMI. Check the unit toggle.

4. Reading One Point as a Diagnosis

A single percentile is a screen. Diagnosis needs a clinician who sees the growth trend and the whole child.

5. Using It Under Age 2

BMI-for-age does not apply under 2. Clinicians use the WHO weight-for-length chart there.

6. Expecting It to Judge Fitness

BMI cannot tell muscle from fat, so a muscular teen may read high without excess body fat.

The tool follows the published CDC formula and holds the full CDC LMS table, so the arithmetic reproduces the CDC percentile for a given BMI, sex and age. The limits are in what a percentile can tell you.

This is not a diagnosis. Discuss any concern about a child growth with a pediatrician.

The CDC lists the 5th to below the 85th percentile as a healthy weight for ages 2 to 19. Below the 5th is underweight, and the 85th or above is overweight or obesity.

Healthy body fatness changes with age and differs by sex during childhood. The CDC ranks a child BMI against others of the same sex and age, rather than using fixed adult cut points.

It means the BMI is higher than about 85 percent of children of the same sex and age in the CDC reference group. The CDC marks the 85th to below the 95th percentile as overweight.

The tool computes BMI, looks up the CDC L, M and S values for the child sex and age, finds a z-score with z = ((BMI/M)^L - 1) / (L x S), then converts it to a percentile with the normal distribution.

Yes. You can enter kilograms and centimetres or pounds and inches. The tool converts pounds at 0.45359237 kg and inches at 2.54 cm before computing BMI.

Ages 2 to 19, which is 24 to 240.5 months. Under age 2, clinicians use the WHO weight-for-length chart. For adults, use the adult BMI calculator.

No. It is a screening estimate from one measurement. A pediatrician interprets it with the growth trend over time and the whole child, and only a clinician can diagnose.

It is how many standard deviations a BMI sits from the median for that sex and age. A z-score of 0 is the 50th percentile, and 1.645 is the 95th percentile.

BMI changes quickly in childhood, so the CDC data is given by month. Adding the extra months to the years gives a more exact percentile than using whole years.

The CDC describes it as a BMI at or above 120 percent of the 95th percentile, or 35 kg/m2 or higher, using separate extended charts. This tool reports the standard categories and does not label severe obesity.

No. The math runs in your browser. Anything you Save stays only in your own browser storage.

• SAS Program for CDC Growth Charts (z-score and percentile formula) (CDC, Last Reviewed 2024-09-25; accessed 2026-10-04).
• CDC BMI-for-age LMS data file (bmiagerev.csv) (CDC, 439 rows / 219 per sex; accessed 2026-10-04).
• Child and Teen BMI Categories (CDC, Last Reviewed 2024-06-28; accessed 2026-10-04).
• CDC Growth Charts Data Files (CDC, Last Reviewed 2024-09-02; accessed 2026-10-04).