Food & nutrition

Growth charts: percentiles, trajectories, prematurity, and what a change means

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A growth chart compares a child’s measured body size with age- and sex-specific reference curves. A percentile is a rank within that reference, not a percentage of ideal size or a test score. Weight, height, head circumference and BMI answer different questions; their interpretation depends on the chart, accurate measurements and the pattern over time.[1]

Choose the measurement before the percentile

Measures used for different purposes
Measure	What it helps describe
Length or height for age	Linear growth and current tallness or shortness.[1]
Weight for age	Body weight relative to age; in older children it does not classify underweight or overweight by itself.[1]
Weight for length or BMI for age	Weight relative to body length, or age-specific BMI; the two indices are not interchangeable.[5]

A reference and a standard have different origins

WHO’s multicountry study collected data from approximately 8,500 children in six countries, including Brazil, Ghana, India, Norway, Oman and the US. The standard was designed to describe physiological growth in supportive conditions, with breastfeeding as the normative model. CDC’s US reference largely describes attained size from national survey data. These are constructed comparison tools, not predictions that every healthy child must follow the median line.[3]

The chart changes with age and jurisdiction

For US practice, CDC recommends WHO standards from birth to two years and CDC 2000 charts for children two and older. The 2022 extended BMI charts cover very high BMIs, above the 97th percentile, with additional curves rather than extrapolating an older chart beyond its intended range. These are US recommendations; other countries’ clinical systems can use different charts or cutoffs. Record which chart and index were used before comparing visits.[4]

Changing charts can change the rank

At age two, US practice changes from recumbent length to standing height and often from weight-for-length to BMI-for-age. CDC notes that standing height is about 0.8 centimetres shorter than recumbent length; reference populations and cutoffs change too. A percentile shift during this transition can arise without sudden physical deterioration. Compare the actual measurements, index and earlier trajectory, and interpret the transition cautiously.[5]

Use the developmental starting point

For an infant born early, chronological age is time since birth, while corrected age describes age from the original due date. Nationwide Children’s explains use of corrected age for plotting through about two years, with some experts extending this to three. Not correcting can make growth appear suboptimal. Weight, length and head circumference should be considered together; prematurity, birth weight and health affect catch-up patterns.[6]

Evidence & uncertainty

Growth charts screen and monitor; they do not independently diagnose the reason for an unusual measurement. CDC’s methods report distinguishes attained size from growth velocity. Repeated measurements reveal progress, while clinical assessment also considers feeding, illness, development and family context. A single low or high percentile is not a complete conclusion.[2]

Selected-source overview · Independent review pending

Published questions

Does the twentieth percentile mean twenty percent of normal growth?

Selected-source overview · Independent review pending. Read the evidence context.

No. A percentile gives a position within an age- and sex-specific reference distribution. It does not measure percentage of ideal size. Different measurements provide different information, so a weight rank cannot substitute for a height or BMI interpretation.[1]

Evidence behind this answer

Anthropometric Indices: Definitions and Categories
official guidance · Date not stated
Original official guidance relevant sections inspected · Definitions, percentiles and difference between weight-for-age and BMI-for-age