Child height predictor
Mid-parental height from the parents' heights, shown with the range it actually spans.
Average the parents' heights, then add 6.5 cm for a boy or subtract 6.5 cm for a girl. It has been used in paediatrics for decades and its limits are just as well established: actual adult height scatters about 8–9 cm either side of it. A single midpoint reads like a promise, so the range is shown alongside.
Parents' heights
What you enter is saved in this browser, so it is still here next time
Adds 6.5cm to the parents' average.
Predicted adult height
Mid-parental height
175 cm
Usual range
166.5 cm – 183.5 cm
±8.5cm
± 8.5 cm
The midpoint alone is not accurate. The band is 17cm wide, which makes this the rough genetic range rather than a prediction.
Based on the parents' heights only. Nutrition, sleep, illness and the timing of puberty decide the actual figure, and growth concerns need a paediatrician.
One formula, four numbers
For a boy: (father's height + mother's height + 13) ÷ 2. For a girl: (father's + mother's − 13) ÷ 2. The 13 is twice 6.5, the average difference between adult men and women assumed when the formula was set up. With the defaults of 175 cm and 162 cm a boy comes to 175.0 cm and a girl to 162.0 cm — the parents happen to differ by exactly 13 cm, so the son matches the father and the daughter the mother. Change the parents to 180 cm and 165 cm and a boy is 179.0 cm. Raising one parent by 2 cm moves the answer by only 1 cm, because the two are averaged.
±8.5 cm is a band taken from statistics
The screen shows 8.5 cm either side of the midpoint, a band 17 cm wide. When the formula was applied to large groups, roughly nine in ten adult heights fell inside that band, and it is the width paediatrics commonly uses. It also means one in ten fell outside. For the default boy the band is 166.5–183.5 cm. The screen does not narrow or widen the band for an individual child — it is not given any data that would justify doing so.
Where the result is commonly misread
The midpoint is not a promise of how a child will grow; it is the average over many children of parents with these heights. Siblings get the same predicted height and end up at different ones. The value depends on the parents alone, not on the child's age or current height, so being taller or shorter than peers today is not reflected in it. The sex choice only decides whether 13 cm is added or subtracted. Heights can be entered to one decimal place and are shown rounded to one.
What this screen does not look at
It takes no current height, weight, age, bone age or timing of puberty. The Tanner paper cited as the source predicts from height and bone age, as its title says; this screen uses only the mid-parental part. Nutrition, sleep and illness shape the actual figure, and there is nowhere to enter those either. What comes out is therefore a statistical estimate, not a diagnosis. If a child's growth is on your mind, the right step is a growth chart and a paediatrician.
Common questions
QHow accurate is it?
The midpoint alone is not accurate. Roughly nine in ten fall within ±8.5 cm — but that band is 17 cm wide, which makes this less a prediction than the rough genetic range. Nutrition, sleep, illness and the timing of puberty decide where inside it a child lands.
QHow is this different from a growth chart percentile?
This looks only at the parents; a growth chart looks at where the child stands among peers right now. When the two disagree sharply — a tall predicted height with a low current percentile, say — that is the point at which a paediatrician is worth seeing. This screen does not replace that.