Genetic Height Potential
Two parents’ heights give you a range that adult heights in that family tend to fall in. It is a fact about the parents, not a forecast about a child — and this page shows you the range, the reasoning, and everything the method cannot tell you.
It is about the parents
The only inputs are two adult heights. That is genuinely all the mid-parental method uses — which is why every child of the same two parents gets the same answer.
A range, not a number
You get a span of about 17 cm, because that is how precise this method actually is. Anyone showing you a single confident figure has rounded away the uncertainty, not removed it.
The limits are on the page
What this explains, what it misses, and where the error comes from — written out below rather than tucked into a footnote. Free, and no email needed to see your result.
How this is worked out
It is the mid-parental method your pediatrician would recognise, published by Tanner. For a male child, add 13 cm to the mother’s height; for a female child, subtract 13 cm from the father’s height — that is the average adult height difference between the sexes — and then average the two heights. Take roughly two standard deviations either side of that average, which is the ±8.5 cm that produces the range you see. That span covers about the 3rd to the 97th centile of adult heights associated with those two parents.
We show whole centimetres and whole inches. The input is a self-reported adult height, and a number derived from that does not carry a decimal place worth printing.
Why we do not ask about the child
We do not ask for anything about the child — no height, no weight, no age. The standard method that uses a child’s own measurements (Khamis-Roche) has no coefficients below age 4, so there is nothing honest to do with them for a younger child. Adding boxes for numbers we cannot use would make the answer look better informed than it is.
What this cannot tell you
- It explains about a third of the answer
- Mid-parental height accounts for roughly 36% of the variation in adult height. Nutrition, health, timing of puberty and ordinary genetic reshuffling account for the rest — which is why the range below is as wide as it is. A narrower range would be a nicer product and a worse answer.
- Your own heights are probably a little off
- In a pediatric endocrinology clinic, only about 50% of fathers and 58% of mothers reported their own height within 2 cm of measured, and roughly one in seven was off by more than 4 cm. That error goes straight into the range. If you have been measured recently, use that number.
- The classic formula runs slightly low
- Children land on average about 2.7 cm taller than this formula suggests, partly because each generation has grown taller than the last. We show the standard formula rather than a corrected one, so the number is the one your pediatrician would recognise — but read it knowing it leans a little short.
- A newborn’s own size tells you almost nothing
- Birth length explains only about 7–9% of adult height, and birth weight under 0.1%. So there is no version of this that gets sharper by adding your baby’s measurements — the information is not there yet.
Sources: Tanner et al. for the mid-parental method and the target-height range; Khamis & Roche (Pediatrics, 1994) for the 4.0–17.5 year validity window of the standard non-radiographic prediction method; pooled twin-cohort analysis for the birth-length figure; Hermanussen et al. for variance explained and the parental self-report error rates.