How Much of Your Height Is Genetic?
You will see the figure everywhere: height is about 80% genetic. It is broadly correct and almost universally misread. Understanding what that number actually measures changes how you should read any height prediction — including the one this site produces — and it explains the two things parents find most puzzling: why tall couples have average children, and why a whole country can grow ten centimetres in a lifetime.
What heritability actually measures
Heritability is a statement about a population, not a person. When researchers say height is 80% heritable, they mean: of all the variation in adult height across the group studied, about 80% of it can be attributed to genetic differences between those people, and about 20% to everything else.
It does not mean 140 cm of your height came from your genes and 35 cm from your dinners. Heritability cannot be divided up inside one individual. Every centimetre of you required both a genetic instruction and the nutrition to execute it — the way a building's height requires both blueprints and bricks, with no sensible way to say the third floor came from the drawings.
There is a further consequence that surprises people: heritability changes with the environment. In a population where every child is well fed, nutrition varies little, so almost all the remaining differences trace to genes and heritability measures high. In a population where some children go hungry, environment explains much more of the spread and heritability measures lower. The same trait, the same species, a different number — because the statistic describes a group's circumstances as much as its biology.
There is no height gene
Height is polygenic. Genome-wide association studies have now linked more than ten thousand common variants to adult height, and the large majority contribute well under a millimetre each. No single switch decides the outcome; thousands of small nudges add up.
This is why height blends smoothly through a family instead of arriving in discrete versions, and why it forms the familiar bell curve in any population. It is also why direct-to-consumer genetic tests still predict adult height less accurately than simply measuring both parents — the parental measurement silently captures the entire genetic contribution, including the parts no study has mapped yet.
Why tall parents get shorter children
The main mechanism is regression to the mean, and it is a statistical effect rather than a biological one.
An unusually tall adult is typically tall for two reasons at once: a genuinely strong genetic endowment, and a favourable roll of the dice — good childhood nutrition, no serious illness during growth, a lucky combination of variants. Only the first of those is inherited. The child receives the genetic endowment, then takes their own roll of the dice, which is on average unremarkable.
So children of very tall parents are usually tall, but on average closer to the population mean than their parents. The same effect runs in reverse: children of very short parents tend, on average, to be slightly taller than their parents. Both are consequences of the same arithmetic.
Layered on top is sibling variation. Each child inherits a different random half of each parent's genes, so siblings sample the same pool differently. Adult height differences of eight to ten centimetres between brothers are entirely ordinary — which, incidentally, is the ceiling on how precise any parents-only prediction can ever be. The mid-parental formula returns a band about 17 cm wide for exactly this reason.
The 20%: what environment can and cannot do
The clearest evidence that environment matters comes from history rather than the laboratory. Over the twentieth century, average adult height in South Korea, Japan and the Netherlands rose by roughly a decimetre. The Dutch went from among the shorter populations in Europe to the tallest in the world. No gene pool changes that fast — what changed was childhood nutrition, disease burden, sanitation and healthcare.
The right way to read this is that environment does not add height beyond a person's genetic potential; a poor environment subtracts from it. Those populations were not exceeding their genetics, they were finally reaching them.
What can subtract, in rough order of impact:
- Chronic undernutrition during growth — insufficient total energy or protein over months and years, not a few skipped meals.
- Untreated chronic illness — coeliac disease, inflammatory bowel disease, poorly controlled asthma, kidney disease, untreated hypothyroidism.
- Sustained sleep deprivation through the growth years — the largest pulses of growth hormone are released during deep sleep.
- Repeated serious infection — the historical driver behind most population-level height gaps.
- Very early puberty — not a deficit but a timing effect, ending growth sooner and reducing the final total.
Note what is absent: for a healthy, adequately fed child, no supplement, stretching routine or exercise programme adds height beyond genetic potential. The realistic goal is not to exceed the ceiling but to avoid falling short of it.
What this means for predicting a child's height
Three practical conclusions follow, and they shape how this site reports results.
- Parental heights are the single strongest input. They capture the whole genetic contribution in two numbers, including everything genetics research has not yet identified.
- They cannot be enough on their own. Because each child samples the family gene pool differently, parents alone yield a wide band. Narrowing it requires information about the specific child — current height for age and how far through puberty they are.
- A single number is a false promise. Any honest prediction is an interval, and its width should vary: wider for young children with most of puberty ahead of them, narrower for adolescents already close to finished.
The calculator on this page follows that logic — parental heights for the genetic centre, the child's own trajectory to adjust it, and an interval that widens or narrows according to age, pubertal stage and how much the two methods disagree.
Frequently asked questions
How much of height is genetic?
In well-nourished populations, about 80% of the variation between people traces to genetic differences. It is a statement about a population, not about an individual — it does not mean 80% of your height came from your genes and 20% from your diet.
Is there a single gene for height?
No. Height is polygenic, with more than ten thousand common variants identified, most contributing under a millimetre each. That is why it blends smoothly through families rather than appearing in distinct versions.
Why do tall parents sometimes have a shorter child?
Chiefly regression to the mean. Very tall adults are tall through both strong genetics and favourable circumstances, and only the genetics passes on. Sibling variation adds to it, since each child inherits a different random sample of the same pool.
Can nutrition really change adult height?
It can lower it substantially and can let someone reach potential they would otherwise miss, but it cannot exceed the genetic ceiling. Average heights in South Korea, Japan and the Netherlands rose by around a decimetre in a century — far too fast for genetic change.
If height is mostly genetic, why do predictions still miss?
Because a child inherits a random half of each parent's genes, not their average. Parental heights capture the family's centre but not which combination a given child received — hence siblings finishing ten centimetres apart, and a prediction band around 17 cm wide from parents alone.
This page is general information for parents and carers, not medical advice, diagnosis or treatment. If you are concerned about your child's growth, speak to a paediatrician or family doctor.