How Percentiles Work
Growth percentiles compare your child's measurements to a reference population of children the same age and sex. A child at the 50th percentile is at the midpoint — half of children measure above, half below. Percentiles between the 5th and 95th are generally considered within the normal range.
Pediatricians use percentiles to track growth trends over time, not to diagnose from a single measurement. A child who consistently tracks along the 15th percentile is typically growing normally. What matters clinically is when a child's percentile shifts significantly between visits — crossing two or more major percentile lines may warrant evaluation.
Standards Used
This calculator follows the approach recommended by the CDC and endorsed by the American Academy of Pediatrics (AAP):
- For children under 24 months, calculations use the WHO Child Growth Standards (2006) — prescriptive standards based on healthy breastfed infants from six countries, describing how children should grow under optimal conditions.
- For children 2 years and older, calculations use the CDC 2000 Clinical Growth Charts — reference data based on US national health surveys, describing how children typically grew.
- BMI percentiles are calculated for children 2 years and older only. For children under 2, the WHO recommends weight-for-length as the appropriate indicator.
- All percentiles are computed using the LMS method (Box-Cox transformation), the standard statistical approach used in clinical practice worldwide.
References
WHO Growth Standards: WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards. Geneva: WHO, 2006.
who.int/tools/child-growth-standards
CDC Recommendation: Grummer-Strawn LM, et al. Use of WHO and CDC Growth Charts for Children Aged 0–59 Months. MMWR Recomm Rep. 2010;59(RR-9):1–15.
CDC MMWR RR-5909a1
CDC Growth Charts: Kuczmarski RJ, et al. 2000 CDC Growth Charts for the United States: Methods and Development. Vital Health Stat 11(246). 2002.
CDC Clinical Growth Charts
Growth percentiles are a screening reference, not a diagnosis. Always consult your pediatrician for clinical interpretation.