See where your child falls on the official WHO and CDC growth charts for weight, height, head circumference and BMI — with a plain-English read on what it means.
A growth percentile answers one simple question: out of 100 children of the same age and sex, how many would measure less than yours? If your baby is in the 60th percentile for weight, they weigh more than about 60 of those 100 children and less than the other 40. The 50th percentile is simply the median — the middle of the pack — not a goal to hit or a grade to beat.
This is the single most important thing to understand: there is no "good" or "bad" percentile. Healthy, thriving children sit all across the chart, from the 3rd percentile to the 97th. A petite baby at the 10th percentile who is feeding well, meeting milestones and following their own curve is every bit as healthy as a big baby at the 90th. Percentiles describe variety; they don't rank it.
Percentile = the share of same-age, same-sex children who measure below your child.
Not all growth charts are the same. This calculator follows the exact combination the CDC recommends for children in the United States: the WHO standards for the first two years, then the CDC charts after that.
| Chart | Age range | Based on | What it describes |
|---|---|---|---|
| WHO Child Growth Standards | Birth to 24 months | Healthy, breastfed babies across six countries under optimal conditions | How children should grow — a prescriptive standard |
| CDC Growth Charts | 2 to 20 years | A large US reference sample from national surveys | How children in the US do grow — a descriptive reference |
Why switch at age 2? The WHO standards are based on optimally-nourished infants and are considered the better yardstick for early growth, including for breastfed babies. By age 2, the two charts line up closely and the CDC reference carries growth tracking through childhood and the teen years. For head circumference, only the birth-to-24-month WHO data is used, since head growth is most clinically useful in that early window.
Growth charts aren't just curves on a page — behind each one is a set of three numbers for every age and sex, known as the LMS parameters (L for the skew of the distribution, M for the median, and S for the coefficient of variation). This tool uses the official published LMS values from the WHO and CDC and applies the standard formula to turn your child's measurement into an exact z-score, then a percentile. It's the same math your pediatrician's software uses to plot a dot on the chart.
Everything runs privately in your browser — nothing you type is stored or sent anywhere. For the most accurate result, weigh your baby without a diaper, measure length lying down for children under 2 (and standing height from age 2), and enter their age as precisely as you can, since percentiles shift week to week in infancy.
Pediatricians rarely worry about a single measurement. What they watch is the trajectory — whether your child is tracking steadily along a percentile band over months. Babies often settle onto their own curve in the first year or two, and a gradual shift as they find it can be completely normal. Growth also comes in spurts, so two measurements close together can look surprisingly different.
What's more worth a conversation is a sudden, sustained crossing of two or more percentile lines up or down, a flattening of weight gain, or a measurement far from a child's usual pattern. Even then, it's information to explore, not a diagnosis. Feeding changes, illness, prematurity and genetics all shape the picture, which is exactly why your provider interprets growth alongside everything else they know about your child.
Bring growth up at your regular well-child visits, and reach out sooner if you notice: a large drop or jump across percentile lines; weight gain that has clearly stalled; a baby who seems persistently hungry, lethargic or is having very few wet diapers; or a head circumference that's changing unusually fast. These don't automatically signal a problem, but they're the kinds of patterns worth a professional eye. Trust your instincts — you know your child best, and no calculator replaces the reassurance of an in-person check.
The 25th percentile means that, among 100 babies of the same age and sex, about 25 would measure less than yours and about 75 would measure more. It is not a grade or a score — it simply describes where your child sits in the normal range. A healthy baby can sit at the 5th percentile or the 95th; what matters more is that they keep growing steadily along their own curve over time.
Both, following the standard US guidance. For children under 24 months it uses the World Health Organization (WHO) Child Growth Standards, which describe how healthy, breastfed babies grow under optimal conditions. From age 2 (24 months) through 20 years it switches to the CDC growth charts. The Centers for Disease Control and Prevention recommend exactly this combination for US children.
Usually not on its own. Children come in a wide range of healthy sizes, and a single number rarely tells the whole story. Pediatricians pay closest attention to the trend — whether your child is following their curve — rather than one measurement. A large, sustained jump or drop across percentile lines, or very poor weight gain, is worth discussing with your provider, but a stable low or high percentile is often just your child's normal.
The math itself is exact — this tool uses the official WHO and CDC LMS parameters, the same statistical values clinicians use to plot growth charts. The accuracy of your result depends mostly on the accuracy of your measurements. Weighing without a diaper, measuring length lying down for babies under 2 and standing height after that, and using a precise age all matter. Your pediatrician measures under controlled conditions, so treat this as a helpful estimate.
It matters a little. Babies under 2 are measured lying down (recumbent length), while children 2 and older are measured standing (height), and standing measurements run slightly shorter. The WHO and CDC charts are built for these conventions, so this calculator expects length under 24 months and height from age 2. Measuring the other way can shift the percentile by a few points.