Growth charts turn a raw weight and length into a comparison against thousands of healthy infants. But percentiles are easy to misread — they describe where a baby sits, not how well they're doing.
What the WHO curves are
The WHO growth standards were built from healthy, breastfed infants across many countries, describing growth under optimal conditions. Comparing against them shows how a baby stacks up to that healthy reference population.
Reading a percentile correctly
A percentile is a position, not a score. Being at the 20th or 80th percentile is both normal — health shows up in steady progress along a channel, not in hitting a particular number. That's why pediatricians track the curve over time.
When it matters
Persistent crossing of percentile lines, or measurements far outside the range, are what flag attention. Context — birth size, genetics, prematurity — always shapes interpretation, which is why the clinician's eye beats a single chart point.
Frequently asked questions
It's where your baby sits relative to other healthy babies of the same age and sex — e.g. the 40th percentile for weight means bigger than 40% of peers. It's not a grade.
No — any point between roughly the 3rd and 97th percentile can be perfectly healthy. The pattern over time matters far more than any single measurement.
A steady channel is typical. Rapidly crossing several lines in one direction can be a reason to check in with your pediatrician, who can look at the full picture.