Behind every percentile is a calculation — the WHO LMS method — that compares your child to a large reference population. Understanding it removes the mystery.
Percentile and z-score
A percentile says where your child ranks; a z-score says how far from the median in standard deviations. Both come from the same WHO reference tables.
The LMS method
WHO tables encode three values per age — L (skew), M (median), and S (spread) — that let any measurement be placed precisely on the curve. This is the same math pediatricians use.
Why the reference matters
The WHO Child Growth Standards are used for ages 0–5 and the WHO Growth Reference for older children. Using the wrong table can shift results — the app always uses the right one.
Let the calculator do the work
GrowChart computes percentiles and z-scores from the official WHO tables the moment you log a measurement, so the math is always correct and always the right reference.
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