How this calculator works
The CDC 2000 reference supplies sex-specific L, M and S values. Exact ages between published half-month rows use linear interpolation of those parameters, as allowed by CDC. The calculation describes a position in that reference population. Repeated accurate measurements and clinical context matter more than one point. This page covers standing height and weight references from age 2 through the 20th-birthday endpoint. Infant length and weight comparisons are available on the baby percentile page. Weight-for-age does not distinguish body fat from height or build. The result is an estimate for information only and is not medical advice.
Formula
z = ((X/M)^L - 1)/(L x S), or ln(X/M)/S when L = 0. Percentile = 100 x Phi(z), where Phi is the standard normal cumulative distribution.
Worked example
A boy aged exactly 24 months weighing 12.6707633 kg is at the reference median: z = 0 and percentile = 50%.
Frequently asked questions
What does the 50th percentile mean?
The measurement equals the reference median for the selected age and chart sex. Half the reference distribution lies below it.
Can a percentile diagnose a growth problem?
No. Measurement technique, health history and the pattern over time need assessment by a health professional.
Which units and ages can I use?
Age accepts months, years or days. The reference range is 24 to 240 months. Lengths convert to centimetres and weight to kilograms before the LMS calculation.