"He's only on the 15th percentile, is that bad?" Faced with the growth chart, many parents worry about a number that, on its own, means very little. Here's how to read and interpret that curve calmly.
What is a growth chart?
A growth chart is a graph that tracks your child's weight, length and head circumference month by month. It compares their measurements with the World Health Organization (WHO) standards and shows their percentile.
These WHO charts, built from thousands of healthy children around the world, are the reference for young children, in the United States, the CDC and AAP recommend the WHO growth standards for children under 2 years. Separate charts exist for girls and boys, because growth differs.
How to read a percentile
A percentile places your child among 100 children of the same age and sex.
For example, if your baby's weight is on the 85th percentile, it means 85 children out of 100 are lighter, and 15 are heavier. On the 25th percentile, 25% are lighter and 75% heavier.
The 50th percentile is the median (the "average"). The range usually considered normal runs from the 3rd to the 97th percentile. But a percentile alone doesn't tell you whether a child is thriving: it all comes down to consistency.
What matters most: the channel, not the number
Here's the key to interpretation: a baby who steadily follows their own "channel" is growing normally, whether on the 10th, 50th or 90th percentile.
A child sitting steadily around the 15th percentile, alert and active, has no "delay": they're simply smaller than average, often in line with family genetics. What does deserve a doctor's attention is:
- a break in the curve (the child suddenly jumps channels, up or down);
- a curve that flattens (growth stalls);
- a marked, unexplained change.
Note: during the first two or three years, it can be normal to shift channels while a child settles onto their own curve. These pointers are for information only and don't replace your pediatrician, who alone can interpret the curve in full context.
Weight, length, head circumference: three complementary curves
You never look at weight alone. Three measurements are read together:
- weight-for-age;
- length (or height)-for-age;
- head circumference, especially important in the first year as it reflects brain growth.
It's the consistency between these curves and their trend over time that gives a reliable picture.
Track growth, simply
Plotting measurements, finding last month's value, seeing the trend… the paper health record allows it, but between visits you quickly lose track.
On Ambrette, growth tracking is free: log your baby's weight, length and head circumference, and the app automatically plots their curves against WHO standards. You see the trend at a glance, share it with your co-parent, and arrive at the pediatric visit with a clear history. Your data stays private and is never sold.
To go further, read How much milk by age? and the pediatric appointment checklist.
Frequently asked questions
What is a percentile on a growth chart?
A percentile shows where your child stands among 100 children of the same age and sex. At the 25th percentile, 25% of children are smaller or lighter and 75% are bigger or heavier. No percentile is "good" or "bad" on its own.
My baby is on the 10th percentile, should I worry?
Not in itself. A child who steadily follows their own channel (10th, 25th…) is growing normally, even below average. What matters is the consistency of the curve over time, not a single point. If the curve breaks sharply, talk to your pediatrician.
How often should I measure my baby?
At well-child visits (close together in the early months, then spaced out), the health professional weighs and measures your baby and plots the values. There's no need for frequent weigh-ins at home: it's the trend across several measurements that counts, not a single value.
Sources
- World Health Organization (WHO), Child Growth Standards.
- Centers for Disease Control and Prevention (CDC), Using WHO Growth Standard Charts.
