Kids BMI Percentile Calculator

Pick the sex. Boys and girls have separate reference curves, because body fat changes differently for each as they grow. Choose Boy.

Enter age in years. The arrows move in whole years from 2 to 13, but you can type a decimal such as 10.5. The tool multiplies by 12, so 10 becomes 120 months. Age matters more than most parents expect. With the same 32 kg and 140 cm, this boy is at the 43.8th percentile at age 10, the 38.6th at 10.5 and the 33.4th at 11. Healthy BMI rises through these years, so typing the age at his last birthday for a child who is nearly a year older makes the percentile read several points high. Entering 13 or more shows an out-of-range message instead of a result.

Enter weight and height in metric. Use 32 kg and 140 cm. If you have pounds and inches, multiply pounds by 0.4536 and inches by 2.54. Measure height without shoes and weight in light clothing. A 2 cm error in height changes BMI by about 3 percent.

Read the results. The panel shows BMI 16.3, a 43.8th percentile and Healthy weight. The percentile means his BMI is higher than about 44 percent of 10-year-old boys in the CDC reference population. It does not mean 44 percent of anything is wrong or right.

BMI = weight (kg) ÷ height (m)².

LMS parameters. For each sex and age, the CDC 2000 BMI-for-age charts publish three numbers. L is the Box-Cox power that corrects for skew, M is the median BMI, and S is the coefficient of variation. The tool's table runs from 24 to 155.5 months at half-month points. For an age between two points, it interpolates L, M and S in a straight line.

z-score = ((BMI ÷ M)^L − 1) ÷ (L × S). If L is zero this becomes z = ln(BMI ÷ M) ÷ S. This is Cole's LMS transformation, the method behind the CDC charts.

Percentile = Φ(z) × 100, where Φ is the standard normal cumulative distribution. The tool uses the Abramowitz-Stegun approximation and clamps results to between 0.01 and 99.99.

95th-percentile BMI = M × (1 + L × S × 1.645)^(1/L), where 1.645 is the z-score of the 95th percentile. Severe obesity is flagged when BMI is at least 120 percent of that value or at least 35, whichever is lower. That is the definition used in the American Academy of Pediatrics' 2023 Clinical Practice Guideline on childhood obesity.

For the 10-year-old boy, z = −0.155 gives the 43.8th percentile. His 95th-percentile BMI is 22.1, so the severe-obesity line would be 26.5.

An 8-year-old girl who weighs 25 kg and is 128 cm tall has a BMI of 15.3, a z-score of −0.32 and a percentile of 37.5, which is healthy weight. Her BMI is a full point lower than the boy's, yet her percentile is similar. Each child is compared only with children of the same age and sex.

Keep her height at 128 cm and change the weight. At 22 kg, BMI is 13.4, the 4.0th percentile, which is underweight. At 31 kg, BMI is 18.9, the 89.0th percentile, which is overweight. For a child this size, 9 kg covers three bands. That is why the CDC treats the cut-offs as screening points that call for a closer look, not as labels.

For the boy at 140 cm, 45 kg gives BMI 23.0, the 96.2nd percentile and obesity. That is 104 percent of his 95th-percentile BMI and still below the 26.5 severe-obesity line. For a 6-year-old boy at 116 cm and 30 kg, BMI is 22.3, the tool shows the 99.6th percentile, and the result is severe obesity. His BMI is 121 percent of the 95th-percentile value of 18.4.

The CDC 2000 charts were built largely from national survey data collected before childhood obesity became common, and their curves stop at the 97th percentile. In December 2022 the CDC released extended BMI-for-age growth charts. They keep every percentile up to the 95th exactly as it was in 2000. Above that, they add curves up to the 99.99th percentile, built from more recent survey data with updated methods. The CDC now advises against using the 2000 charts for children above the 97th percentile.

This calculator does not use the extended curves. Below the 95th percentile its results match both chart sets. Above the 95th it still uses the 2000 LMS formula, so a displayed figure such as the 6-year-old's 99.6th percentile should not be taken literally. At that level, clinicians usually describe BMI as a percent of the 95th percentile, and this page reports that figure for the examples. The tool's severe-obesity label uses the same 120 percent or BMI 35 rule as the extended charts and the AAP guideline. It does not show the higher class that starts at 140 percent.

Children usually follow their own curve, and a stable line is reassuring even near either edge of the chart. The more useful signal is a change in direction. That might be a climb across the 85th and 95th percentile lines over a couple of years, or a sudden drop after an illness. One measurement taken at home can't show either.

Timing also matters. BMI normally falls in early childhood and then rises again, a pattern called adiposity rebound, and puberty starts at different ages. A child who matures early can look heavier for a while compared with peers. Muscular, athletic children can also have a high BMI without extra body fat. That is why the next step after a high or low screening result is a visit to the doctor, not a diet. Restricting a growing child's food without medical guidance can do harm.

The tool covers ages 2 years to 12 years 11 months only. The CDC recommends WHO growth charts for children under 2, and for teenagers the doctor's full CDC chart runs to age 20. Its reference population is American. It does not use the 2022 extended percentiles, so anything above the 97th percentile is approximate. BMI measures weight for height, not body fat. The results may not suit children whose growth is shaped by a medical condition, such as Down syndrome, which has its own specialised growth charts. It is a screening estimate for parents, never a diagnosis.

BMI-for-age is only one of the CDC growth charts. The child growth percentile calculator reads height-for-age and weight-for-age percentiles from the same CDC 2000 reference data for ages 2 to 20, which helps show whether a BMI change comes from growth in height or from weight. Once a young person reaches adulthood, the percentile method stops and fixed cut-offs apply. The BMI calculator uses the adult 18.5, 25 and 30 thresholds, and the BMI calculation guide explains why those numbers work for grown adults but not for a child whose healthy BMI is still changing. The ideal weight calculator is also an adult tool. Its height-based formulas assume growth has finished, so use it for parents and older teens who have stopped growing, and use this page for younger children.