How Child BMI Percentile Differs From Adult BMI
Adult BMI uses fixed cutoffs — 25 and up means overweight, no matter your age. But growing kids have body fat percentages that naturally shift with age and sex, so pediatricians use a BMI-for-age percentile instead, comparing your child to same-age, same-sex peers on CDC growth charts. This calculator takes age, sex, height, and weight to estimate that percentile and classify it into one of four categories.
How the percentile bands work
Below the 5th percentile is classified as underweight, 5th-85th as healthy weight, 85th-95th as overweight, and 95th and above as obese. BMI naturally rises and falls around puberty (the "adiposity rebound"), so tracking the trend over several months is more meaningful than any single measurement.
Talk to a professional for an accurate diagnosis
This calculator uses representative age-based averages and standard deviations, so it's an approximation and may differ from the exact CDC growth chart your pediatrician uses. If your child falls in the overweight or obese range, avoid making sudden diet or activity changes on your own — a pediatrician can give an accurate diagnosis and management plan.
Frequently Asked Questions
Growing children's body fat percentage naturally changes with age and sex, so instead of fixed adult cutoffs, kids are assessed with a percentile compared to same-age, same-sex peers.
No. This calculator gives a reference estimate only. An accurate assessment considers growth velocity, build, and family history — please consult a pediatrician.