Growth Charts and Percentiles Explained

At almost every checkup, your child is weighed and measured, and the numbers are plotted on a growth chart. Then you hear something like "she's in the 30th percentile for height." What does that mean, and should you be worried if the number seems low or high? This guide explains how growth charts work, why the pattern over time matters more than any single point, and when growth is a reason to look more closely.

What gets measured

Your pediatrician tracks a few key measurements:

• Weight at every visit.
• Length or height. Babies and toddlers under 2 are measured lying down (length). Older children are measured standing (height).
• Head size, measured around the head, during the first 2 to 3 years. This helps track brain growth.
• Weight compared with length for babies under 2, and body mass index (BMI) from age 2 on.

Each measurement is plotted against your child's age, and boys and girls have separate charts.

What a percentile means

A percentile compares your child with a large group of children of the same age and sex. If your son is at the 40th percentile for weight, it means that out of 100 boys his age, about 40 weigh less than he does and about 60 weigh more.

A percentile is not a grade or a score. The 90th percentile is not "better" than the 10th. Healthy children come in all sizes, and a child can be perfectly healthy anywhere across a wide range of percentiles. A small child with small parents who is growing steadily at the 10th percentile is usually doing just fine.

Two kinds of charts, by age

In the United States, pediatricians generally use two sets of charts:

• From birth to age 2: the World Health Organization (WHO) charts. These are based on healthy babies around the world who were raised in good conditions, most of them breastfed. They show how babies grow when their needs are well met.
• From age 2 on: the CDC charts. These are based on measurements of children in the United States and are used through the teen years, including BMI-for-age.

Babies who were born early are often tracked using their adjusted age, which counts from their due date instead of their birth date, for the first couple of years. Children with certain conditions, such as Down syndrome, may also be followed on special charts.

The trend matters more than one number

A single measurement is a snapshot. A growth chart is more like a movie. What your pediatrician cares about most is the line that connects the dots from visit to visit.

• Most children follow their own curve. After the first year or two, many children settle into a percentile range and stay near it.
• Some shifting is normal early on. In the first 2 years, babies often move up or down a bit as they find the size their genes intend. A big baby with shorter parents may drift down; a small newborn may catch up.
• Measurements can be off. A wiggly baby, a heavy diaper, shoes or a cowlick can throw off one reading. One odd point is often re-measured rather than acted on.
• Puberty changes the timing. Children who start puberty earlier or later than their friends may move across percentiles for a while before settling.

When growth may be a concern

Your pediatrician will look more closely when the pattern changes in certain ways, such as:

• Crossing two or more major percentile lines, either up or down, after infancy.
• Weight dropping or stalling, sometimes called faltering weight or failure to thrive, especially in babies and toddlers.
• Height slowing down while weight keeps rising, or height falling away from the curve.
• Measurements far outside the usual range, such as below the 3rd percentile or very high, especially if they do not match the family's build.
• Head size growing much faster or slower than expected.
• Weight rising much faster than height, leading to a BMI that climbs into the overweight or obesity range.

A change in the pattern does not always mean something is wrong. Often there is a simple reason, like a recent illness, a feeding challenge or a growth spurt. Your pediatrician will ask about eating, sleep, activity, health history and the heights of parents and siblings. Sometimes the next step is simply to measure again in a few weeks or months. In other cases, blood tests, a bone age X-ray or a visit with a specialist may help.

How you can help

• Keep up with well visits. Regular measurements are what make the growth curve useful.
• Know your family history. Share both parents' heights and any family history of early or late puberty, growth problems or thyroid conditions.
• Ask to see the chart. Your pediatrician can show you your child's curve and explain where they are headed.
• Avoid comparing. Siblings, cousins and classmates grow on their own schedules.
• Focus on habits. Balanced meals, active play and enough sleep support healthy growth for every body type.

You can read more about normal growth and development on MedlinePlus, about faltering weight in young children, and about growth disorders.

When to call us

Call your A thru Z Pediatrics office if your baby is not feeding well or seems to be losing weight, if your child's clothes and shoes have stopped getting tight for a long time, if your child seems much shorter than classmates and is not catching up, if they show signs of puberty very early or very late, or if you notice a fast change in weight. Call right away if a baby has fewer wet diapers than usual, is very sleepy, or will not feed.

Call 911 or go to the ER if your child is hard to wake, has trouble breathing, or shows signs of serious dehydration, such as no urine for many hours, a dry mouth and no tears.

To go over your child's growth chart with us, request a visit.