Predicting adult height from parental height
Height is one of the most strongly heritable physical traits — research consistently finds parental height explains a large share of the variation in adult height between people. The mid-parental height method takes advantage of this, offering a simple estimate using nothing but both parents' heights.
Boys: (father's height + mother's height + 13) ÷ 2
Girls: (father's height + mother's height − 13) ÷ 2
The 13cm adjustment reflects the average height gap between adult men and women, applied in the direction appropriate to the child's sex after averaging both parents' heights together.
What this method can't capture
Height has a genetic component, but it isn't determined solely by genetics. Childhood nutrition, chronic illness, sleep, and overall health all influence whether a child reaches their genetic height potential. This formula assumes reasonably typical conditions and can't account for significant deviations in any of these factors.
A rough estimate, not a guarantee
Research validating this method against actual adult outcomes finds a margin of error of roughly ±8.5cm — meaningful enough that the predicted number should be treated as a reasonable ballpark, not a precise forecast. It's a fun, genuinely science-based estimate rather than a clinical growth assessment.