Infant growth (WHO 0 to 24 months)

Weight-for-age, length-for-age, weight-for-length, and head circumference-for-age percentiles and z-scores with the CDC-recommended 2nd and 98th percentile cutoffs.

Version 0.1.0

Inputs

SexUsed by the equation
Age from
Chronological age, birth to 24 months
Optional. Corrects age when below 37 weeks
weeks
Optional
Optional
Optional

Sex, weight is shared with every calculator.

When to use
  • Infants and toddlers from birth to 24 months (CDC recommends the WHO standards under 2 years).
  • Length should be recumbent length.
Pearls and pitfalls
  • CDC uses the 2.3rd and 97.7th percentiles (z of ±2), labeled the 2nd and 98th, as cutoffs for low and high values on WHO charts.
  • For infants born before 37 weeks, enter gestational age to plot by corrected age, usually until 24 months chronological age.
  • Weight-for-length is independent of age and covers 45 to 110 cm.
  • One measurement is a snapshot: crossing two major percentile lines or a falling trajectory matters more than a single value.
Formula

z = ((X/M)^L − 1) ÷ (L × S); percentile = Φ(z). Weight indicators beyond ±3 SD use the WHO restricted method: z = ±3 + (X − SD3) ÷ (SD3 − SD2). Corrected age = age − (40 − gestational age) weeks

Evidence

  1. Primary WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards based on length/height, weight and age. Acta Paediatr Suppl. 2006;450:76-85. PubMed 16817681
  2. Guideline Grummer-Strawn LM, Reinold C, Krebs NF. Use of World Health Organization and CDC growth charts for children aged 0-59 months in the United States. MMWR Recomm Rep. 2010;59(RR-9):1-15. PubMed 20829749

Reference data: CDC growth chart data files and CDC-hosted WHO Child Growth Standards tables (public domain). API: POST /api/v1/calculate/growth-who with sex, ageMo (months), and measurements.

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