Child BMI calculator

It compares the child with others of the same age and sex. At the 60th percentile, the child's BMI is higher than 60 out of 100 children in the reference.

On the CDC charts, the healthy range runs from the 5th up to the 85th percentile. The 85th to 95th is overweight, the 95th and above obese and under the 5th underweight; the WHO charts draw their lines in standard deviations instead.

It is worked out the same way, weight in kilograms divided by height in metres squared, but read differently: as a percentile against children of the same age and sex, never against the adult 18.5, 25 and 30 lines. A healthy BMI changes as a child grows, and from 20 the adult categories apply.

They are the same position on two scales. The z-score counts standard deviations from the median for age and sex, and the percentile turns it into a rank out of 100: 0 is the 50th percentile, +1 about the 84th and +2 about the 98th.

Use what your paediatrician uses: the CDC charts in the United States, the WHO charts in most other countries. They draw the lines differently, so the category can differ between them.

Children and teens from 2 to 19. The CDC charts go up to the 20th birthday and the WHO charts up to the 19th; for adults, use the BMI calculator.