Child Growth Percentile Calculator (LMS Method)
Estimate a child's height or weight percentile using the real LMS statistical method behind official growth charts — entirely in your browser.
Processed entirely in your browser — nothing you enter here is ever uploaded.
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About this tool
When a pediatrician says a child is "in the 60th percentile" for height or weight, they mean a statistical position on that measurement's population distribution for the child's exact age and sex — not a grade or a target. This calculator computes that position with the real technique used to build official growth charts, called the LMS method, entirely in your browser: nothing you enter is uploaded anywhere.
LMS stands for the three parameters that describe the distribution of a measurement at a given age: L (a Box–Cox power that captures the skewness of the distribution), M (the median) and S (the coefficient of variation, roughly how spread out values are). From these, a measurement is converted into a z-score with a closed-form formula: z = ((value / M)^L − 1) / (L × S) when L is not zero, or z = ln(value / M) / S in the special case where L = 0. That z-score is then converted into a percentile with the standard normal cumulative distribution function, which this tool implements as a genuine numerical approximation (Abramowitz & Stegun's rational formula), not a lookup table.
Honesty matters more than polish here: authoring the complete, byte-exact official WHO or CDC LMS reference tables — which list separate L, M and S values for every month of age — by hand is not something this tool can responsibly claim to have done. Instead it bundles a small, internally consistent set of illustrative L/M/S rows, one every 12 months from birth to 20 years, for boys and girls, for height-for-age and weight-for-age, shaped to follow realistic pediatric growth curves (a decelerating infant growth rate, a visible adolescent growth spurt, a median that plateaus near typical adult height and weight). The calculator linearly interpolates between the two nearest bundled ages for whatever exact age you enter — the same interpolation approach real growth-chart software uses — but the underlying numbers are a teaching approximation, not the official chart. For a clinically precise percentile, use your pediatrician's official WHO or CDC chart.
Use this tool to understand how the LMS method actually works and to get a reasonable, illustrative sense of where a measurement sits — not as a medical result. It is not medical advice and cannot replace your pediatrician's growth assessment, which uses validated reference data and considers your child's full growth history, not a single measurement. Everything here runs locally: no age, sex or measurement is ever sent to a server or stored.
Example. A boy at 120 months whose height is 137.8 cm matches the bundled median and returns the 50th percentile.
Limit. LMS rows exist only every 12 months from birth to 240 months, and those rows are an illustrative curve rather than the official WHO or CDC tables.