See Baby's Growth Curve

A growth percentile tells you how your child's size compares to other children of the same age and sex. For example, if your baby is at the 40th percentile for weight, that means 40% of babies weigh less and 60% weigh more. The 50th percentile is simply the median — it is not a passing grade or a target. A wide range of percentiles is perfectly normal. A child at the 10th percentile can be just as healthy as one at the 90th. What matters most is your child's own trend over time. Pediatricians look for a consistent growth curve rather than a single number, so tracking measurements at regular intervals gives the most useful picture.

Two major growth references are used in the United States: the World Health Organization (WHO) charts and the Centers for Disease Control and Prevention (CDC) charts. The WHO charts are based on an international study of healthy, breastfed children and describe how children should grow under optimal conditions. The CDC charts are based on a broader sample of the US population and describe how children actually grew during a specific time period. The American Academy of Pediatrics (AAP) recommends using WHO charts for children under 2 years of age and CDC charts for children ages 2 through 20. Akacharts follows this guidance and automatically switches between the two standards based on your child's age. WHO data covers ages 0 to 5 years, while CDC data covers ages 0 to 20 years.

The curved lines on a growth chart represent percentile bands — typically the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97th percentiles. Your child's measurement appears as a point plotted against these curves, showing where they fall relative to the reference population. The z-score shown alongside the percentile is a statistical measure of how far a measurement is from the median. A z-score of 0 means exactly average, while positive values are above average and negative values are below. Most children fall between z-scores of −2 and +2. If your child's measurements cross two or more major percentile lines over time — either upward or downward — it is worth discussing with your pediatrician. A single measurement is just a snapshot; the pattern across multiple visits tells the real story.