WHO vs CDC growth charts: what percentiles mean

What a percentile actually means

A percentile tells you how your child's measurement compares to a reference group of children the same age and sex. If a child is at the 40th percentile for height, that means, in the reference group the chart was built from, about 40 out of 100 children of the same age and sex were the same height or shorter, and about 60 were taller. It is a comparison, not a grade. A child at the 20th percentile who has always tracked near the 20th percentile is typically growing exactly as expected for that child.

Why there are two different charts

The WHO charts and the CDC charts were built for different purposes. The WHO charts are described as growth standards: they describe how healthy children grow under optimal conditions, using data collected from breastfed infants across several countries. The CDC charts are described as a growth reference: they describe how a large sample of children actually grew in the United States at a particular time, which includes both breastfed and formula-fed infants and a broader range of feeding and health circumstances.

Because breastfeeding is the feeding standard recommended for infants, and because breastfed and formula-fed infants tend to grow at somewhat different rates in the first year, using a standard built specifically around the recommended feeding pattern gives a more accurate picture for that age group.

Which chart applies at which age

The CDC and the American Academy of Pediatrics recommend using the WHO growth standards for infants and toddlers from birth to age two, regardless of whether a child is breastfed or formula-fed. At age two, the recommendation switches to CDC's own growth charts, which continue through age twenty. This two-year cutoff isn't arbitrary; it matches the age range each set of charts was actually built to cover.

Because the two charts use somewhat different reference groups, a child's percentile can shift slightly right around the age-two switch, even with no real change in how the child is growing. That's expected, and worth knowing about so it doesn't look alarming on its own.

What a percentile change over time can mean

A single percentile number matters less than the pattern over several measurements. A child who has tracked steadily near the same percentile for months is generally following their own expected growth curve. A percentile that moves sharply, up or down, across two or more visits is the kind of change a pediatrician will usually want to look at more closely, since it can reflect anything from a normal growth spurt to something worth investigating further.

What a single measurement can't tell you

One height or weight measurement, on its own, rarely tells you very much. Growth charts are built to be read as a trend across multiple visits, plotted against age, not as a single data point compared to a target. This is also why measurement conditions matter: a length taken with a squirming infant, or a weight taken in a diaper versus fully dressed, can shift a single point on the chart without reflecting a real change. None of this is a substitute for your pediatrician's own reading of your child's growth. A chart is a tool for a conversation with them, not a diagnosis on its own.