Growth percentiles

What percentiles are

The WHO growth standards describe how healthy children grow from 0 to 5 years. The percentile tells you where your child stands among peers of the same sex: at the 25th weight percentile, for example, they weigh more than 25% of children their age. There is no «right» percentile: what matters is that growth follows its own curve over time.

The data used

LMS-method calculation on the official WHO tables (weight-for-age, length/height-for-age, head circumference-for-age, BMI-for-age). Up to age 2 the reference measure is recumbent length; afterwards, standing height.

Important note

A value outside the common ranges is not a problem by itself, just as an «average» value doesn't rule everything out: the assessment always belongs to your pediatrician, who looks at the overall trend.

A percentile is not a grade

A percentile says how many children of the same age and sex are below that value: at the 25th percentile 25 children in 100 are smaller and 75 are bigger. It is not a scale of merit, and the 50th is not the target: by definition half of all healthy children sit below the median.

Being consistently on the 10th or the 90th percentile is as normal as being on the 50th: the curves describe the variability of healthy children, and the tails are part of normality. A small child of small parents is exactly where they should be.

What matters is the trajectory

A single day's value says little; what paediatricians look at is the curve over time, whether the child keeps growing along the same channel. A child always on the 15th percentile is growing well; one who slides from the 75th to the 25th in a few months deserves attention even while staying «average».

The other signal is the relationship between the curves: weight, length and head circumference tell different stories, and how they relate says more than any of them alone. Weight falling while length keeps rising is not the same thing as both slowing down.

Bad measurements are commoner than problems

Up to two years length is measured lying down, and standing after that: the same child measured both ways differs by about half a centimetre, so at the second birthday the curve has a small step that belongs entirely to the method, not to the growth.

Weight should be taken with no nappy and on the same scales, because two household scales can differ by two or three hundred grams, which on a newborn is a lot. An isolated value that looks wrong should be measured again before worrying: almost always it was the measurement.

Nearby tools

For the age to use in the tables, especially if the baby was born early, there is Baby's age. For an estimate of adult height look at Child's future height.