Child Growth Percentile Calculator

The calculator interpolates WHO reference mean and standard deviation values for weight-for-age at your child's exact age, computes a z-score (how many standard deviations the child's weight is from the reference mean), then converts that z-score into a percentile using the standard normal distribution.

Official WHO and CDC growth charts use LMS (Lambda-Mu-Sigma) parameters that account for skewness in the weight distribution at each age, which is more statistically precise than assuming a simple normal distribution. This calculator uses the simpler normal-distribution approximation for transparency and ease of calculation, which is accurate enough for a general estimate but not identical to official charts.

A weight-for-age percentile shows how a child's weight compares to same-age, same-sex peers in the reference population — the 50th percentile is the reference median, while the 10th percentile means roughly 10% of same-age children weigh less. A single measurement in any percentile range is not inherently good or bad; a consistent growth trend over time matters more than one snapshot.

Not necessarily — children grow at different individual rates, and genetics play a large role. Pediatricians look at the trend across multiple visits (is the child tracking consistently along their own curve?) rather than a single percentile number. Always discuss growth concerns with your child's pediatrician rather than relying on an online estimate alone.