Growth Percentiles
Weight and length percentiles from WHO and CDC tables.
A percentile is a position in a distribution of healthy children. It is not a score, and the number matters far less than the direction.
The 15th percentile means 15 out of 100 healthy babies of that age and sex weigh less. Someone has to be on the 15th. Someone has to be on the 3rd. The curve was built by measuring thousands of healthy, well-fed children, and its whole width describes normal.
What paediatricians actually read
Not the number — the line.
A baby who tracks along the 15th percentile from birth to a year is growing exactly as expected. A baby who was on the 75th at two months and the 25th at six months has crossed two major lines downward, and that is worth a conversation even though 25th is an entirely ordinary percentile to be on.
Crossing one line is usually nothing, especially in the first months when babies commonly settle onto their genetic curve after a birth weight that reflected the pregnancy rather than the child. Crossing two lines in either direction, sustained across more than one visit, is the point at which the trend gets looked at.
Which chart, and why it matters
Two charts are in common use and they are not interchangeable.
WHO standards (0–24 months) describe how healthy, predominantly breastfed children should grow under good conditions — a prescriptive standard. CDC charts (2 years and up) describe how American children did grow in a reference population — a descriptive reference.
Because of that difference, breastfed babies commonly appear to "drop percentiles" after about three months on a CDC chart while tracking perfectly on a WHO one. The CDC itself recommends WHO charts for under-twos in the United States for exactly this reason. If a chart at a clinic is not labelled, it is worth asking which one it is before reading anything into a shift.
Weight alone is the least useful measurement
Three numbers are plotted, not one. Length-for-age and weight-for-age together give weight-for-length, which is what says whether a baby is proportionate. Head circumference tracks brain growth and is the measurement most likely to be quietly checked and least likely to be mentioned.
A single weight, plotted once, tells you almost nothing. That is why the chart has a line on it and not a dot.
Reference tables only. Any concern about your child's growth belongs with your paediatrician, who has the full history this site does not.
5 articles
Weight Percentile for a 6-Month-Old: The WHO Table, and Why the Number Matters Less Than the LineThe 10th percentile is not a problem and the 90th is not an achievement. What a paediatrician actually reads is the direction of travel.
Baby Weight Percentile by Month: WHO Tables for the First YearThe full month-by-month table for the first year. The number it gives you is the least important thing on the page.
How Much Weight Should a Newborn Gain? 5–7 oz a Week After the First FortnightNewborns lose weight before they gain it. Up to ten percent in the first days is expected, and back to birth weight by two weeks is the milestone that matters.
Head Circumference by Age: The Measurement Nobody MentionsIt is taken at every well-baby visit and explained at almost none of them. Head circumference tracks brain growth, and its trend line is watched more closely than weight.
Baby Length by Age: WHO Tables, and Why It Is Measured Lying DownLength is the hardest of the three growth measurements to take accurately, which is why it looks noisier on a chart than it really is.