Child height predictor

Method A uses only parental heights: boys = (father + mother + 13) / 2, girls = (father + mother − 13) / 2, with a ±6.5 cm band, from the Tanner & Whitehouse 1976 mid-parental method. Method B is a simplified Khamis-Roche: the original equation regresses on the child’s current height, weight and mid-parental height (no bone age needed), and this tool follows the same idea by projecting current height through the proportion of adult height already attained and blending that with the parental target.

Because adult men and women differ by roughly 13 cm in average height, and the mid-parental method folds that straight into the formula: boys add 6.5 cm to the parental average and girls subtract 6.5 cm, which is the same as adding or subtracting 13 before halving. That is why, with identical parental heights, the boy’s target height is exactly 13 cm above the girl’s.

They are median approximations from the CDC 2000 growth charts: a 2-year-old boy has reached about 50% of adult height, 83% at age 10 and essentially 100% by 17; girls mature earlier, at about 52% at age 2, 91% at 10 and essentially 100% by 14. These are population values, so early or late puberty shifts the actual timing by a year or two.

It gives a range, not a number. Height is polygenic, and nutrition, sleep, exercise, chronic illness and pubertal timing all matter, so a 3–5 cm gap between the two methods is entirely normal. If a child is well below the 3rd percentile or grows less than 4–5 cm a year, see a paediatric endocrinologist.

Because the Khamis-Roche idea is that current height matters more the closer a child is to adulthood. The tool weights by the proportion of adult height already attained: a small proportion (a young child) leans on the parental target, while a proportion near 1 (late puberty) pulls the prediction towards the child’s current height.