Infant growth chart
The infant growth chart most clinicians use from 0 to 24 months is the WHO Child Growth Standards (2006). The same chart is what AAP, NHS, and most national ministries of health recommend for this age range. The version for parents is sometimes called the "baby growth chart" — it's the same underlying LMS data, just with less technical language.
To compute your infant's percentile right now, use the baby percentile calculator. It plots your measurement on the WHO chart and shows both the percentile and the z-score.
Three infant charts, not one
- Weight-for-age (WFA) — weight at a given chronological age.
- Length-for-age (LFA) — recumbent length at a given age.
- Weight-for-length (WFL) — weight conditional on length, not age. Detects wasting/overweight independent of how old the baby is.
This site covers WFA and LFA for 0–24 months. WFL is useful for acute malnutrition screening and is typically tracked separately in clinical practice.
Percentiles and z-scores
Pediatricians read both. A percentile is the rank in the reference distribution (50th = half are above, half below). A z-score is the number of standard deviations from the median — it keeps being informative past the edges of the chart (below the 3rd or above the 97th) where percentile numbers bunch up. The LMS method is the conversion in both directions.
Clinical thresholds
WHO defines <−2 z-score (roughly the 2nd percentile) as the screening threshold for moderate underweight or stunting, and <−3 as severe. Above the curve, >+2 WFL flags overweight. These thresholds apply to WHO-defined growth failure and don't automatically apply to an otherwise-healthy infant who's simply small or large.
What a single reading means (not much)
Infants jitter on the chart — they gain unevenly around feeds, illness, teething, and sleep regressions. Pediatricians weight trajectory over point-in-time percentile: a baby who tracks along the 10th consistently is usually fine; a baby who drops from the 75th to the 10th over two visits is the one who gets evaluated.
Preterm infants use different charts
For infants born before 37 weeks, the Fenton preterm growth chart or Intergrowth-21st is more appropriate, and corrected age (gestational adjustment) is used in place of chronological age. WHO term-infant charts understate how preterm babies are actually tracking.