At the next paediatric check-up, the doctor points to a chart and says: "Your child is on the 25th percentile." What does that actually mean? Cause for concern — or completely normal?
Growth percentiles are one of the most important tools in paediatrics, yet they are frequently misunderstood. This article explains how they work, what WHO charts measure and how to correctly interpret the numbers for your child.
What Are Growth Percentiles?
A percentile tells you where a measurement sits relative to a reference population. The 25th weight percentile means: 25 % of children of the same age and sex weigh less, 75 % weigh more.
Crucially, a percentile is not a score for how "good" a child is. A child on the 10th height percentile is not shorter than they should be — they are simply shorter than 90 % of their peers, which can perfectly match their genetic make-up.
Key reference percentiles
The normal range spans the 3rd to 97th percentile. Values outside this range are not automatically pathological, but do signal that a closer look may be warranted.
WHO Growth Standards: The Global Reference
In 2006, the World Health Organization published new growth standards for children aged 0–5 years, supplemented in 2007 by reference data up to age 19. These standards are now the worldwide gold standard.
Key distinction: WHO standards describe optimal growth under ideal conditions (breastfed children, non-smoking household, no chronic illness) — not average growth in any given population. They represent a target, not a mere average.
What WHO tracks
0–10 years, boys and girls
0–18 years, boys and girls
2–18 years — more useful than absolute BMI
0–3 years — indicator of brain development
The LMS Method: How Percentiles Are Calculated
WHO charts rely on the LMS method by Cole and Green (1992). It transforms the often skewed distribution of body measurements into a normal distribution, enabling precise percentile calculation.
Three parameters describe the distribution at each age:
The Z-score is then converted to a percentile using the standard normal distribution. A Z-score of 0 is the 50th percentile; a Z-score of −2 is approximately the 2.3rd percentile.
How to Read Growth Charts Correctly
A single measurement is less informative than the trend over time. Two questions matter most:
- 1.Is the child tracking steadily along a curve?
A child consistently on the 10th percentile is likely naturally small — this is normal.
- 2.Is there a sudden drop or jump?
A child falling from the 50th to the 10th percentile needs medical assessment — even though 10th is within the normal range.
When to see a paediatrician
- → Measurement below the 3rd or above the 97th percentile
- → Drop or rise crossing two or more major percentile lines
- → Head circumference growing unusually fast or stalling
- → Large discrepancy between weight and height percentiles
BMI in Children: Different from Adults
The raw BMI number means little in children. A BMI of 17 can be normal for a 4-year-old but signal underweight for a 10-year-old. What matters is always the BMI-for-age percentile.
WHO categories for BMI-for-age
Calculate your child's growth percentiles
Enter age, weight and height — the calculator instantly shows where your child stands on the WHO chart.
Open Child Growth CalculatorSummary
Growth percentiles are not a ranking — they are a tool for understanding your child's individual growth over time. A child on the 10th percentile is not "worse" than one on the 90th: they simply grow differently.
What matters is consistency of the curve. If your child follows their own growth trajectory, everything is fine. Deviations from that trajectory — not the absolute value — are the real signal for a paediatrician.