BMI for boys at 13 years

At 13 years, the median BMI for boys on the CDC 2000 growth charts is 18.4 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 17.0 and 20.4 kg/m², a spread of 3.4 kg/m². The outer lines of CDC’s BMI-for-age chart, the 5th and 95th percentiles, sit at 15.4 and 25.1 kg/m².

Since 12 years, the median has risen by 0.7 kg/m² over 1 year. By 14 years it reaches 19.1 kg/m².

For girls at 13 years the median is 18.7 kg/m², 0.3 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 13 years the 85th percentile for boys is 21.8 and the 95th is 25.1 kg/m². Above the 95th percentile, CDC's 2022 extended charts replace the original curve, so the 99th percentile here is 32.3 kg/m², computed with the extended method.

Reading the table: a boy at 13 years with a BMI of 19.5 kg/m² is at about the 65th percentile, meaning that out of 100 boys this age, about 65 have a lower BMI.