BMI Percentile Chart for Kids and Teens by Age

An adult BMI chart is the wrong tool for anyone under 20. Children and teenagers are scored against CDC BMI-for-age percentiles, where the same number can be healthy at one age and too high at another. This page covers how to calculate BMI for a child, how to read the percentile bands, what changes between ages 2, 10 and 17, and where the reference curves come from. Adults should use the BMI Calculator or read their row in the BMI chart by height instead.

Why Children Get Percentiles Instead of 18.5 to 25

BMI is weight divided by height squared, so the adult bands of 18.5, 25 and 30 assume a finished body. Children are still growing: body fat falls through early childhood, rises again around puberty, and differs between boys and girls at every age. A fixed number cannot describe that, so the CDC plots BMI by single year of age and sex and reports where a child sits against a reference population. Percentile is the number that gets tracked from one visit to the next, and the adult chart does not apply to anyone under 20.

How to Calculate BMI for a Child

• Metric: weight in kilograms divided by height in metres squared. A child who is 1.30 m tall and weighs 27 kg: 1.30 x 1.30 = 1.69, then 27 / 1.69 = 16.0.

• Imperial: weight in pounds divided by height in inches squared, then multiplied by 703. A child who is 51 in tall and weighs 59 lb: 51 x 51 = 2601, then 59 / 2601 = 0.0227, and 0.0227 x 703 = 15.9.

Both routes agree within a rounding step, and both give the same BMI of about 16. The arithmetic is the easy part. What you cannot do next is read that 16 against the adult bands.

Worked Example: Reading a 10-Year-Old's Result

Take a 10-year-old girl who is 135 cm tall and weighs 31 kg. Height in metres is 1.35, squared is 1.8225, and 31 / 1.8225 gives a BMI of 17.0. That 17.0 is now plotted on the CDC BMI-for-age curve for girls at exactly 10 years and 0 months. It is not compared with 18.5, and it is not judged on its own: whether it lands in the healthy band depends on her exact age in months, because the reference distribution shifts with every birthday. This is why two children of the same height and weight can sit in different bands.

The CDC BMI-for-Age Bands

Once the percentile is known, the categories are fixed for every age from 2 to 19:

• Below the 5th percentile — underweight.

• 5th percentile to under 85th percentile — healthy weight.

• 85th percentile to under 95th percentile — overweight.

• 95th percentile and above — obesity.

The CDC also defines severe obesity at 120 percent of the 95th percentile. Percentiles run from 1 to 99, so a child at the 60th percentile is heavier than 60 percent of children of the same age and sex — a statement about ranking, not about health on its own.

What Changes Between Ages 2, 10 and 17

• Ages 2 to 5: BMI is read on the infant and child growth charts, and fatness typically falls to its lowest point around age 4 to 6. This dip before the rise is called the adiposity rebound, and clinicians watch how early it happens.

• Ages 6 to 11: BMI drifts upward gently year by year. Because the reference curves also drift upward, a child can gain weight and stay on the same percentile line at the same time.

• Ages 12 to 19: growth spurts move height and weight at different speeds, so BMI can jump a couple of points within a school year and settle again afterwards. Sex differences in muscle and fat also widen through these years.

Because of that movement, the percentile — not the raw BMI — is what gets compared across visits, and a single reading is always read together with the pattern before it.

Boys and Girls Use Different Charts

There is one CDC chart for boys and one for girls, each split by single year of age from 2 to 19. The same BMI of 19 at age 13 can sit at different percentiles for a boy and a girl. Height is plotted on its own curve as well, so a teenager who has just shot up in height may drop a percentile band without having lost any weight at all.

Where to Read the Percentile

The CDC publishes the reference curves behind every growth chart, and its BMI percentile calculator takes age, sex, height and weight and returns the percentile and the category in one step. Pediatric offices plot the same curves, either on a printed wall chart or in the electronic record. The BMI Calculator on this site is built for adults: it returns the adult category and the healthy weight range for your height, and it should not be used to score a child.

What BMI Cannot Tell You About a Child

BMI-for-age is a screening measure, not a diagnosis. It does not separate muscle from fat, does not describe where fat is carried, and says nothing about nutrition, activity level or family history. A child who is athletic, asthmatic, on medication that affects appetite, or living with a condition that changes growth may plot high or low without it meaning what the raw band implies. Pediatricians therefore read one point on a chart against growth history over time, and treat a change in pattern as the useful signal rather than a single visit.

Where These Figures Come From

The percentile bands above are the CDC definitions used in its 2000 growth charts for the United States, which remain the reference for children aged 2 to 19. The worked examples were calculated from the BMI formula rather than read off a printed chart, so the arithmetic is exact — only the percentile step needs the published curves.

Next Step: if you are an adult checking your own range, use the BMI Calculator for the exact figure and category, or read your height row in the BMI chart by height.