Growth Percentile Calculator

This calculator estimates growth percentiles using the LMS method, the standard statistical technique behind official CDC and WHO growth charts. It draws on two different reference populations depending on Age -- the World Health Organization's Child Growth Standards, published in 2006 from an international sample of healthily-fed infants and toddlers, for 0-60 months (the range WHO's own standards cover), and the CDC's 2000 Growth Charts for the United States from 5-20 years -- because no single published standard spans birth through age 20. For each measurement -- Weight, Height/Length, and BMI (BMI-for-age only computed from age 24 months on) -- the engine looks up three reference parameters for the child's Age and Sex: a median value, a measure of spread, and a skewness correction, then expresses the entered measurement as a standardized distance from that median (a z-score) and converts it to a Percentile. The three measurements are independent of each other: Weight Percentile depends only on Weight, Age, and Sex, and is completely unaffected by Height/Length, and vice versa for Height Percentile -- entering a different height changes nothing about the calculated weight percentile.

Sex matters throughout because reference medians differ meaningfully between boys and girls at every age. Weight Status (Underweight / Normal / Overweight / Obese) is only assigned for children 24 months and older, using BMI Percentile cutoffs at the 5th, 85th, and 95th percentiles -- the same threshold convention used on official CDC growth charts; below 24 months, Weight Status is explicitly reported as not assessed rather than defaulting to "Normal," since BMI-for-age is not a validated screening measure at that age. Because this tool interpolates a reference table rather than plotting on an official chart, treat its output as an estimate for tracking trends between visits, not a replacement for the percentile your pediatrician plots directly from the official CDC or WHO chart at a well-child visit -- always confirm a percentile near or outside the 5th/95th boundary against the official chart.