What is target height?
Mid-parental height (the mid-parent height, or “target height”) is a simple calculation that estimates the adult height a child is genetically expected to reach, based on the mother’s and father’s heights. The logic is intuitive: height is largely inherited, so a child’s expected height clusters around the parents’ heights.
The calculation also accounts for the sex difference. In the most common formula, about 6.5 cm is added to the average of the mother’s and father’s heights for a boy, and the same amount is subtracted for a girl (in practice: add +13 cm for boys or −13 cm for girls to the sum of parental heights, then divide by two).
The uncertainty band: why not a single number?
Target height is not a single precise value but a range. Around the calculated height there is a “familial band” of about ±8.5 cm; the child’s adult height is expected to fall within this band. This width reflects the fact that even children of the same parents can differ in height — the height differences between siblings are everyday proof of this.
For this reason, mid-parental height does not say “my child will be exactly this tall”; it says “genetically, this range is expected”. Its real value is in seeing whether the child’s current growth curve is consistent with this familial target.
How is it used?
Target height is most often used to put a child’s current growth into context. For example, if a child who looks short has a height within the familial target band, this is most likely familial (genetic) short stature and is usually not a cause for concern. By contrast, if the child’s growth curve falls markedly below the familial target, this may warrant further evaluation.
Mid-parental height is a complement to more precise methods (Khamis-Roche, Bayley-Pinneau). Those methods personalise the estimate by also taking into account the child’s own age, height, weight and maturation data; target height provides the genetic framework.
Common mistakes
The most common misconception about mid-parental height is to treat the result as a precise prophecy. In fact the calculation is an expectation carrying a band of about ±8.5 cm around it; even children of the same parents can sit at different points within this band. The second common error is assessing the child’s current percentile without comparing it to the target band; the real information is whether the child’s growth curve is consistent with the familial target.
Another point is entering the parental heights with accurate, real values; estimated or rounded heights shift the result. Mid-parental height also does not include the effect of nutrition, chronic illness or hormonal conditions; these can move the actual adult height away from the target. So target height should be used not on its own, but together with growth monitoring and, where needed, with Khamis-Roche or bone-age-based methods.