Baby Weight Percentile Calculator (WHO)

Enter your baby's sex, age, and weight to see their WHO weight-for-age percentile and z-score — with a plain-language read on what it means.

Birth to 60 months (5 years). Decimals allowed (e.g. 6.5).

What does a weight percentile mean?

A weight-for-age percentile compares your baby's weight to other healthy children of the same age and sex, using the WHO Child Growth Standards. If your baby is in the 40th percentile, it means 40% of babies the same age and sex weigh less, and 60% weigh more.

Anything between the 3rd and 97th percentile is considered a normal range. A single number is not a grade — a baby on the 15th percentile can be perfectly healthy. What matters most is the trend: a baby who steadily follows their own curve over time is usually growing well, even if that curve sits low or high.

The z-score is the same information in standard-deviation units: 0 is the median (50th percentile), −2 is roughly the 2nd percentile, and +2 is roughly the 98th. Doctors often track z-scores because they stay meaningful at the extremes.

For more on healthy weight gain in the first year, read our guide to the WHO baby weight chart and first-year weight gain.

How we calculate

We use the WHO LMS method. For each age and sex, WHO publishes three values — L (skew), M (median), and S (coefficient of variation). The z-score is z = ((weight / M)^L − 1) / (L × S), and the percentile is the standard-normal probability of that z-score. We interpolate between the monthly WHO reference points to match your baby's exact age. Data covers birth to 60 months (0–5 years).

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General information, not a diagnosis

This tool is for general information only and does not replace a medical evaluation. Percentiles are one piece of a much bigger picture — feeding, activity, family build, and overall health all matter. If you have any concern about your child's weight or growth, see your pediatrician. Book a consultation with a Babynama pediatrician.