How to Read Your Baby's Road to Health Chart (and What the Percentiles Mean)

Every baby in South Africa gets a Road to Health book, the little booklet the clinic plots your child's weight, length and head size in at each visit. Those curves and dots tell you a lot, but only if you know how to read them, and a low line worries far more parents than it should. Here is what the chart is actually showing, what the percentiles mean, and when a reading is worth a closer look.

What the lines and percentiles mean

The Road to Health growth charts are built on the World Health Organization Child Growth Standards, so they show how your child compares to healthy children the same age and sex, right across the world. Each curved line is a percentile. If your child sits on the 30th percentile for weight, it means that out of 100 children their age, about 30 weigh less and 70 weigh more. The middle line, the 50th percentile, is simply the median, the middle of the range, not a target every child should reach.

A percentile is a ranking, not a mark out of a hundred. The 20th percentile is not a fail and the 90th is not a prize, they are just positions in a normal spread. Two children can both be perfectly healthy, one on the 15th percentile and one on the 85th, because children come in different builds just as adults do.

Is my baby underweight, or overweight?

On the WHO charts, anywhere between the 3rd and the 97th percentile is treated as the normal range. So a baby on the 10th percentile is usually just fine, and being low on the chart is not the same as being underweight. What actually matters is not the single number but the trend, whether your child keeps following roughly their own line over time. A baby who has always tracked along the 15th percentile is typically thriving, while one who has dropped suddenly from the 50th toward the 10th is worth a closer look, even though both numbers sit inside the normal range.

The same is true at the top. A single high weight reading does not mean a child is overweight, and weight on its own cannot tell you that anyway, it has to be read against height. This is why the clinic looks at the whole picture over several visits rather than reacting to one dot.

Check your child's percentile

Enter your child's weight, height or head size and get the percentile in plain language, on the same WHO charts as the Road to Health book.

Open the Child Growth Percentile Calculator →

When a reading is worth a closer look

Reading the chart is really about spotting a change in the pattern, not a low or high number on its own. It is worth speaking to your nurse or doctor if your child's measurement falls below the 3rd percentile or climbs above the 97th, or if their line crosses downward through the percentiles from one visit to the next, for example slipping from the 50th toward the 10th. These can be completely normal, but they can also be the earliest sign that something needs attention, which is exactly what the Road to Health book is designed to catch. Take the book to every visit so the clinic can see the whole trend, not just today's weight.

How to measure at home

If you want to check between clinic visits, small errors change the percentile, so measure carefully. For weight, use a baby or bathroom scale with as little clothing as possible, and no nappy for young babies. For length, babies under two are measured lying down and older children standing up, which is why the chart calls it length or height. For head circumference, run a soft tape around the widest part of the head, above the eyebrows and ears. If a reading looks surprising, measure again, and remember the clinic's measurement is the one to trust.

Turn a measurement into a percentile

Our free child growth percentile calculator uses the same WHO standards as the Road to Health book, so you can enter your child's weight, height or head size and see exactly where they sit, with a plain explanation and an honest flag when a reading is worth checking with the clinic. When your little one is due for their next round of jabs, the child immunisation schedule calculator turns their birthday into the full South African vaccine timeline.

Open the Child Growth Percentile Calculator →

This is general information based on the World Health Organization Child Growth Standards, the same standards behind South Africa's Road to Health book, not medical advice. A single measurement says little on its own, growth is best judged by the trend over time, so always have your child assessed at the clinic if you are worried. Last reviewed July 2026.