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A genetic estimate only; nutrition, health and normal variation mean real adult heights spread widely around it. If you have concerns about a child's growth, their growth chart at the GP or health visitor is the proper tool.
What The Child Height Predictor Works Out
- Predicted adult height: the mid-parental method paediatricians use as a quick estimate. Add the parents' heights, add 13cm for a boy or subtract 13cm for a girl (the average adult height gap between the sexes), then halve. Parents of 165cm and 180cm point to about 179cm for a son and 166cm for a daughter.
- Likely range: plus or minus 8.5cm around the estimate, which covers most children. Height is influenced by hundreds of genes plus nutrition, sleep and general health, so it is a genetic target, not a promise.
- Method: the formula used, shown so you can check the arithmetic.
- Child's age and height now (advanced): a second method scales the child's current height by the share of adult height typically reached at that age. Boys are at about half their adult height at 2 and 78% at 10; girls at 53% at 2 and 84% at 10 because they mature earlier. Doubling height at age two is the folk version of this.
- Blended estimate (advanced): the average of the parental and current-height methods, which is usually closer than either alone once the child is past toddlerhood.
- Growth still to come (advanced): the projected adult height minus today's height, assuming the child stays on the same centile line.
- Parents' heights in inches (advanced): enter 5ft 9in as 69 and the calculator converts (1 inch = 2.54cm).
- Range and sex gap (advanced): the 8.5cm range and the 13cm male-female difference are the textbook figures; adjust them if your paediatrician uses different ones.
- Against the UK average adult (advanced): how the estimate compares with the average UK man (about 175cm) or woman (about 162cm). What matters clinically is not the predicted number but the trajectory: children should track roughly along their centile line in the red book, and it is crossing centiles rather than being tall or short that prompts a closer look. This is general information, not medical advice.
Source and further reading: NHS: baby and child height and weight.