Frequently asked questions

No. The reference tables download with the page and every calculation runs in your browser. Nothing you type is sent to a server, and nothing is saved between visits, so closing or reloading the tab clears it. There are no accounts and no email sign-up anywhere on this site.

The only thing recorded is an anonymous count that the tool was used, carrying which measurement type and how many points were plotted, with no ages, no values, and no percentiles in it. There is no way to tie that count back to a visitor. The privacy policy states the same thing in full.

No. A percentile is a rank position in a reference population, not a target. Every band on the chart is occupied by real children from the reference group: ten percent of them sat at or below the 10th percentile, by construction, and ten percent sat at or above the 90th.

The 50th percentile is the middle of the line, not a goal, and half of any healthy reference population sits below it by definition. Because the arithmetic runs through a normal distribution, percentile spacing is also uneven: a small measurement change moves the number a lot near the middle and very little out in the tails, which is why a z-score is often the steadier thing to watch.

No. Babypercentiles draws the published WHO and CDC reference curves and plots the numbers you enter on them. It does not assess, diagnose, or screen anything, and it gives no guidance about feeding or growth. Percentiles describe position in a reference population, not health.

Everything on this site is arithmetic run on two public datasets, plus writing that explains that arithmetic. Deciding what a measurement or a pattern of measurements means for a particular child depends on birth history, feeding, family size, illness, and much else a chart cannot see, which is why that reading belongs with your child's clinician. For the source material, see the CDC growth chart pages at cdc.gov/growthcharts.

Birth to 60 months, for three measurements: weight for age, length or height for age, and head circumference for age, each for boys and for girls. Above 60 months the tool stops, because that is where the tables it loads end.

Weight and length or height use the WHO standard to 24 months and the CDC 2000 charts from 24 to 60 months. Head circumference uses the WHO standard the whole way. The CDC does publish weight and stature references all the way to 20 years; this site loads only the part of them a chart for young children needs.

From the agencies themselves. The curves are drawn from the WHO Child Growth Standards parameter tables and the CDC 2000 Growth Charts data files, downloaded from who.int and cdc.gov, with the exact file URL and the retrieval date recorded next to every table on this site.

Both agencies publish their curves as LMS parameters: L, a power that accounts for skew, M, the median, and S, the coefficient of variation, given at each age. Those published values are reproduced here exactly as printed, and every percentile shown is computed from them at the moment you ask, never copied from a third party's compiled table. The reference tables page lists every dataset with its source.

Because US practice reads two different references. Birth through 24 completed months uses the WHO Child Growth Standards, and 24 months onward uses the CDC 2000 Growth Charts, following the CDC's 2010 recommendation. They describe different populations, so the curves step slightly at the seam.

The measurement changes at the same age too: under two a child is measured lying down, which is recumbent length, and from two standing, which is stature, and a standing measurement reads shorter. The chart tool marks the seam with a labelled line instead of smoothing it away, and head circumference stays on the WHO standard at every age because the CDC charts carry no head-circumference reference past 36 months.