Child Health Club · Free Tool
Baby Growth Percentile Calculator
Enter your baby’s age, weight, and height to see where they fall on the official WHO growth curves — the same standard pediatricians use.
Check your baby’s growth
Works for babies and children from birth to 5 years, based on WHO Child Growth Standards.
Tracking growth regularly? A reliable baby scale for home use makes weekly check-ins easy between pediatrician visits. (affiliate link)
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How this calculator works
No need to trust a black box — here’s exactly what’s happening.
This tool uses the World Health Organization’s Child Growth Standards, built from healthy, breastfed children across six countries. Every age has three published reference numbers — L, M, and S — that describe the shape of the growth distribution at that exact age. Your child’s measurement is converted into a z-score using those numbers, and the z-score is converted into a percentile: the share of children in the reference population who measure less than your child does.
A percentile is not a grade. The 40th percentile for weight is just as healthy as the 90th — it simply describes where a single measurement sits on a population curve. What usually matters more to a pediatrician is the trend across visits, not any one number in isolation.
Frequently asked questions
Is a low percentile a problem?
Not on its own. Genetics, feeding style, and prematurity all shift where a healthy baby sits
on the curve. Pediatricians watch for a baby who is consistently tracking far outside the
3rd–97th percentile range, or who drops across two or more major percentile bands between visits.
Why does the tool ask for exact age in months?
WHO growth references are built month-by-month for the first two years, since growth is
fastest and most variable in early infancy. A one-month difference in age can shift the
reference curve meaningfully.
WHO vs. CDC charts — what’s the difference?
WHO charts (used here) describe how breastfed infants grow under optimal conditions and are
recommended by the American Academy of Pediatrics for children under 2. CDC charts, used more
often after age 2, are based on how children in the U.S. actually grew historically.