Teen BMI Calculator (Girls)

Adolescence introduces significant physiological changes that render standard adult BMI calculations inaccurate for girls aged 13 to 19. During this window, hormonal shifts drive essential fat deposition required for menstruation and reproductive health. Misinterpreting these natural fluctuations as excess weight often leads to unnecessary dietary restrictions.

This tool utilizes CDC BMI-for-age growth charts specifically calibrated for females in the 13-19 age bracket. Unlike generic calculators, it accounts for the non-linear velocity of pubertal growth. The calculation determines the Body Mass Index percentile, indicating relative position among peers of the exact same age in months. Accuracy here provides a safeguard against eating disorders by validating normal developmental weight gain.

The core calculation utilizes the LMS method (Lambda-Mu-Sigma) to normalize the distribution of BMI for age. The Z-score (Standard Deviation Score) is derived first:

Where L (Box-Cox power), M (Median), and S (Coefficient of Variation) are age-specific parameters from CDC tables. The percentile is then calculated from the Z-score using the standard normal cumulative distribution function.