How to Predict Your Child's Adult Height

The most widely used quick estimate is the mid-parental height formula. You average the mother's and father's heights, then adjust for the child's sex. For a boy, you add about 6.5 centimeters, roughly 2.5 inches, to that average. For a girl, you subtract the same amount. The result is a target adult height.

The reasoning is straightforward: a child's genetic potential is strongly tied to both parents, and the sex adjustment accounts for the average height difference between men and women. It is the same back-of-the-envelope method many pediatricians reach for during a routine visit.

The formula produces a single number, but real outcomes scatter around it. A common rule is that most children land within about 10 centimeters, roughly 4 inches, above or below the predicted height. That is why the estimate is best understood as the center of a range rather than a precise forecast.

This width is normal and expected. Two siblings with the same parents can finish noticeably different heights, and either can fall toward the top or bottom of the predicted band without anything being wrong.

You only need both parents' heights and the child's sex to get an estimate.

Genetics set the broad potential, but they are not the whole story. Nutrition, overall health, sleep, physical activity, and the timing of puberty all influence how much of that potential a child reaches. An early or late growth spurt can shift the picture, which is one reason predictions made in early childhood are less certain.

Certain medical conditions and some medications also affect growth. The formula assumes a generally healthy child with a typical growth pattern, so it will be less reliable when that assumption does not hold.

This calculator is an educational estimate, not a medical diagnosis. If you are worried that a child is much shorter or taller than peers, is growing very slowly, or has crossed several percentile lines on their growth chart, that is a conversation for a pediatrician. A doctor can track growth over time, check for underlying causes, and, when needed, order a bone-age assessment that predicts adult height far more precisely than any formula.