There is no “right” percentile. What the numbers mean, the range doctors use, and the changes that actually matter.
Short answer: there is no percentile your baby should be. Any steady position between roughly the 3rd and the 97th percentile is within the usual range on the WHO growth charts, and healthy babies are found all along it. A baby at the 10th percentile is not doing worse than one at the 90th.
The 50th percentile is the median, not a target. By definition half of healthy babies are below it. On the WHO standard the median weight at 6 months is 7.3 kg (16.1 lb) for girls and 7.9 kg (17.5 lb) for boys, but a 6-month-old girl at 6.4 kg (about the 15th percentile) or 8.3 kg (about the 85th) is just as typical.
Genes set much of where a baby sits. Babies of tall parents tend to track higher for length; babies of smaller parents tend to track lower. In the first year many babies drift a little up or down before settling on their own curve.
What doctors look for instead: a measurement below the 2.3rd or above the 97.7th percentile on the WHO chart for children under 2 (the CDC’s suggested cut-offs, about two standard deviations from the median); a curve that crosses two of the main percentile lines over a few months; or weight and length moving very differently, for example weight dropping across lines while length stays put.
Weight-for-length matters too. A baby at the 20th percentile for weight and the 20th for length is in proportion. A baby at the 20th for weight and the 80th for length is long and lean, which can be fine but is worth watching over time.
One measurement is a snapshot. Home scales, wet diapers and wriggling can move a result by several percentile points. If a number worries you, measure again and compare with the measurements from checkups.
Premature babies should be plotted at their corrected age until about 2. Using their actual age makes them look smaller than they are.
To see where your baby is right now, use the free Growthling percentile calculator. To see the curve, log each checkup in Growthling and it plots them on the WHO or CDC chart.
Sources: WHO Child Growth Standards; CDC, “Use of World Health Organization and CDC Growth Charts for Children Aged 0–59 Months in the United States” (MMWR, 2010). This article is general information, not medical advice.
This article is for informational purposes only and is not a substitute for professional medical advice. Always consult your pediatrician about your child's growth and development.
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