BMI-for-age is a different tool from a weight percentile. It compares weight to height, so it tells a more balanced story about body proportions — but for babies it is never read alone.
What BMI-for-age measures
BMI combines weight and length into one number, then the WHO curve places it against healthy children of the same age and sex. A high BMI percentile means a child is heavy for their length, not that they are 'overweight' in an adult sense.
Read it with the other curves
In the first two years a baby's body shape changes constantly. Pediatricians interpret BMI-for-age together with weight-for-age, length-for-age, and head circumference — one curve never decides anything alone.
The trend beats the number
A single high or low BMI percentile is rarely meaningful. A BMI percentile climbing steadily across visits while length stays flat is the pattern worth discussing; one reading is not.
See all four curves together
GrowChart plots weight, length, BMI, and head circumference on the WHO standards so you and your pediatrician can read the whole picture at each visit.
Try the free calculator
No sign-up needed — check a percentile or z-score in seconds, then save & track when you create a free account.
Open the calculator → Create a free account