Baby percentile calculator (0–24 months)
Get your baby's weight and length percentiles from birth to 24 months using the WHO Child
Growth Standards — the reference recommended by WHO, AAP, and NHS for infants. Percentiles
compare your baby to a healthy population of the same age and sex; the 50th percentile is
the median.
Enter birth date, measurement date, sex, and weight and/or length below. Length should be
measured lying down (recumbent length), not standing. The calculator defaults to "Auto",
which uses WHO under 24 months and switches to CDC after; you can change this in the
Standard dropdown if your clinician prefers a different reference.
Frequently asked questions
What age range does this cover?
Birth to 24 months. The calculator uses the WHO Child Growth Standards by default under 24 months — that's what WHO, AAP, and NHS recommend for infants.
Should I measure length lying down or standing?
Lying down (recumbent length) for under 24 months. WHO length-for-age charts assume recumbent measurement. Stature (standing) is used from 24 months onward.
My baby dropped two percentile bands — should I worry?
A crossing of more than two major percentile lines (e.g. 75th down to below 25th) over a few visits is a reason to bring it up with your pediatrician, but many healthy babies cross percentiles in the first 18 months as they 'canalize' to their genetic trajectory. A single measurement in isolation rarely means much.
Is this accurate for premature babies?
No — for babies born before 37 weeks, you need to adjust for gestational age (corrected age), and under roughly 3 months corrected age the Fenton or Intergrowth-21st preterm charts are more appropriate. This calculator uses term-infant WHO/CDC data.