BMI for boys at 9 years

At 9 years, the median BMI for boys on the CDC 2000 growth charts is 16.1 kg/m²: half of boys this age have a lower BMI and half a higher one. The middle half of boys, from the 25th to the 75th percentile, falls between 15.1 and 17.6 kg/m², a spread of 2.5 kg/m². The outer lines of CDC’s BMI-for-age chart, the 5th and 95th percentiles, sit at 14.0 and 21.0 kg/m².

Since 8 years, the median has risen by 0.4 kg/m² over 1 year. By 10 years it reaches 16.6 kg/m².

For girls at 9 years the median is 16.3 kg/m², 0.1 kg/m² more than for boys, which is why the charts are drawn separately by sex.

CDC uses BMI-for-age, not weight-for-length, from age 2. At 9 years the 85th percentile for boys is 18.6 and the 95th is 21.0 kg/m². Above the 95th percentile, CDC's 2022 extended charts replace the original curve, so the 99th percentile here is 26.6 kg/m², computed with the extended method.

Reading the table: a boy at 9 years with a BMI of 17.0 kg/m² is at about the 67th percentile, meaning that out of 100 boys this age, about 67 have a lower BMI.