BMI Calculator for Kids and Teens

A BMI of 18 can be healthy for a 15 year old and high for an 8 year old, because children's body fat changes as they grow and differs between boys and girls. That is why adult BMI lines such as 23 or 25 are never used for children. Instead the BMI is placed on a growth chart for the child's exact age and sex. This page does that from 5 years to 19 years, using the published WHO and IAP tables, with no chart reading by eye.

The WHO 2007 growth reference for 5 to 19 years is the chart WHO uses worldwide. The page works out the z-score with the WHO LMS method, including the WHO rule for values beyond 3 SD, and turns it into a percentile. WHO calls a z-score above +1 overweight, above +2 obesity, below -2 thinness and below -3 severe thinness. At 19 years the +1 line is close to an adult BMI of 25, so the child chart joins the adult scale. For a boy of exactly 10 years the WHO median is 16.4, overweight starts above 18.5 and obesity above 21.4.

Indian children were found to carry more body fat at the same BMI, so the Indian Academy of Pediatrics revised its charts in 2015 using data on over 33,000 children from 14 cities. For ages 5 to 18 the IAP recommends two cut-off lines: the one that joins an adult BMI of 23 marks overweight, and the one that joins 27 marks obesity. For a boy of 10 these are 18.0 and 20.5; for a girl of 10 they are 18.4 and 21.9. The page reads the IAP table every half year and fills in the months between, and also says which centile lines the BMI falls between.

Because the two charts are built differently, they can disagree near the lines. A boy of 10 with a BMI of 18.2 is overweight on the IAP chart but still normal on the WHO chart. Both readings are shown so you can see why, and your paediatrician can decide which chart to follow. Under 5 years, IAP and WHO use the WHO Child Growth Standards with weight-for-height, which this page does not cover. For 19 and above, switch to Adult.

Your child's age, sex, height and weight are worked out in this browser tab and never leave it. Nothing is uploaded, saved or shared, and there is no sign-up. We count only anonymous events such as the button being pressed, never the numbers.

A single BMI reading is a screening step, not a diagnosis. Children grow in spurts, so the trend over several measurements tells more than one number. Measure height without shoes and weight in light clothes. If the reading is above the overweight line or below the thinness line, talk to your paediatrician before changing a child's diet.