It's one of those questions you probably can't help asking from the moment a baby arrives. Will she have her dad's tall frame? Will he stay small like his mum's side of the family? You scan your children for clues, compare photos across generations, looking for a pattern that explains what you're seeing.
The truth is that height is one of the most studied traits in all of human genetics, and the science behind it is far more interesting than a simple "tall parent, tall child" rule. Children regularly end up significantly taller or shorter than both parents, and identical twins can even differ in height. Understanding why takes us into the world of polygenic inheritance, regression to the mean, and the role of environment. It also starts to explain why height prediction is genuinely tricky, even for scientists.
Height isn't controlled by one gene. It's controlled by thousands.
For a long time, researchers assumed height would be relatively simple to decode genetically. It's easy to measure, clearly heritable, and has been studied for over a century. But what they found as technology improved was anything but simple.
In 2022, an international collaboration called the GIANT Consortium published what remains the largest genetic study of height ever conducted. Analysing genomic data from nearly 5.4 million people, they identified 12,111 genetic variants — specific places in the DNA code where small differences between people are linked to differences in height.[1]
"First we found one gene variant linked to height. Then we found ten. Then there were a couple hundred," said Dr Joel Hirschhorn, the Harvard geneticist who led the GIANT Consortium for over a decade. By the time the 2022 study was complete, they had essentially mapped all of the common genetic regions that influence height.[2]
Height is what scientists call a polygenic trait, a characteristic shaped not by one or two genes but by the combined, cumulative effect of thousands of tiny genetic differences. Each individual variant has a very small effect on its own. It is only when you add them all together that a meaningful pattern emerges. This is why you cannot simply look at a single gene and say "this is the tall gene."
The US National Library of Medicine summarises it clearly: because height is determined by multiple gene variants through polygenic inheritance, it is difficult to accurately predict how tall a child will be, since different combinations of variants can cause siblings to differ in height even though they share the same parents.[3]
So why do tall parents often have tall children?
Even though no single gene determines height, parental height is still the single best predictor we have for a child's adult stature. The reason is straightforward: your child inherits approximately half of their DNA from each parent, so they also inherit a substantial portion of the height influencing variants.
The more variants for greater height both parents carry, the more likely the child is to carry a high number of them too.
This relationship is strong enough to be used clinically. The most widely used method is the midparental height formula, first proposed by paediatrician James Tanner in 1970. It works like this:
For a boy: (mother's height + father's height + 13 cm) ÷ 2
For a girl: (mother's height + father's height − 13 cm) ÷ 2
A 2024 study published in the journal Genes validated this approach in large nuclear families. Using the standard Tanner procedure, midparental height explained 36% of the variance in children's final adult heights, with an estimated heritability of 74%.[4]
A large Swedish population study of 2,402 children found that most children end up within approximately ±10 cm (about ±4 inches) of their predicted target height, and the method works similarly regardless of whether parents have very similar heights or quite different ones.[5]
In clinical practice, a paediatrician reviewing a child's growth chart will typically use the midparental height formula as a reference point. If your child is growing well within the expected range for your family, that's generally reassuring. If they deviate significantly from it, that can be a prompt to investigate further.
Why children are not simply the average of their parents
Here's where things get genuinely surprising. Despite the strong link between parental and child height, children regularly end up noticeably taller or shorter than either parent, or taller or shorter than the simple average would predict. Several well-established mechanisms explain this.
Regression to the mean
This is one of the most important. This statistical principle was first described by Victorian scientist Francis Galton in his landmark 1886 paper, "Regression Towards Mediocrity in Hereditary Stature." Studying 930 adult children from 205 families, Galton found something counterintuitive: the children of unusually tall parents tended to be tall, but not as tall as their parents. The children of unusually short parents tended to be short, but not as short as their parents.[6]
The phenomenon reflects the fact that very tall parents have an unusually favourable combination of height influencing genetic variants. When they pass on their genes, their children receive a random sample, and that sample is statistically less likely to be as extreme in one direction. The result is that heights across a population tend to stay relatively stable over generations, rather than becoming increasingly extreme at either end.
Recombination and chance
When parents pass on their genes, the process is not a neat 50/50 split of identical packages. Chromosomes shuffle and recombine in different ways each time. This means siblings can end up with quite different combinations of height related variants from the same two parents, which is exactly why two children from the same family can be several inches apart in height.
Unexpressed genetic potential
Parents may carry genetic variants that influence height but that they do not fully express themselves, perhaps because of environmental conditions during their own childhood, or because those variants were suppressed by others in their genome. A child who happens to inherit more of these "taller" variants from both parents simultaneously could end up noticeably taller than either parent.
What about the role of the environment?
Genetics sets the ceiling for height, but the environment determines how close your child gets to it. Research estimates that roughly 60 to 80% of height variation between people is attributable to genetic differences, with the remaining 20 to 40% shaped by environmental factors.[7]
The most critical window is infancy and early childhood. A major twin study pooling data from 180,520 paired measurements across 45 cohorts in 20 countries found that shared environmental factors, such as nutrition, health care, and living conditions, have their greatest influence on height in early childhood, though their effect persists into early adulthood.[8]
Nutrition, sleep, physical activity, chronic illness, and even socioeconomic conditions all play a role. A well nourished child growing up in good health is far more likely to reach their genetic potential than one who experiences nutritional deficiencies, illness, or other growth limiting stressors.
So how accurately can we predict your child's height?
The honest answer is: reasonably well, but not precisely. The midparental height formula gives a useful estimate and is the best simple tool available. Most children end up within a few inches of their predicted range. But there are real limitations.
A 2024 analysis in Genes noted that the standard formula tends to underestimate target height slightly, partly because parents shrink in height from their peak as they age. So their measured height at the time your child is being assessed is already lower than their peak adult height.[4]
The formula also does not account for the timing of puberty, which can shift a child's growth trajectory significantly, or for differences in a child's current growth rate and bone development.
For parents curious about their child's likely adult height, a height prediction tool that uses the midparental method can provide a scientifically grounded estimate, while keeping in mind that all such predictions come with a natural range of uncertainty. Genetics is a probability, not a guarantee.
The bottom line
Height is one of the most heritable traits in the human genome, shaped by thousands of genetic variants working together, not a single gene. Parental height is the best single predictor of your child's adult stature, but regression to the mean, genetic recombination, and the environment all mean that surprises are entirely normal. Tall parents having an average height child, or two average height parents having a tall child — these outcomes are not anomalies. They are exactly what the science would expect.
The beauty of polygenic inheritance is that it keeps human height wonderfully variable, generation after generation.
Scientific References
- Yengo L, et al. (2022). A saturated map of common genetic variants associated with human height. Nature, 610(7933), 704–712.
- Hirschhorn, J. (2025). The Genetics of Height. Harvard Medicine Magazine.
- MedlinePlus Genetics, US National Library of Medicine. Is height determined by genetics?
- Zeevi D, et al. (2024). Accurate Prediction of Children's Target Height from Their Mid-Parental Height. Genes, 15(9).
- Luo ZC, Albertsson-Wikland K, Karlberg J. (1998). Target Height as Predicted by Parental Heights in a Population-Based Study. Pediatric Research, 44(4), 563–571.
- Galton F. (1886). Regression Towards Mediocrity in Hereditary Stature. Journal of the Anthropological Institute of Great Britain and Ireland, 15, 246–263.
- Broad Institute of MIT and Harvard. (2022). Largest genome-wide association study ever uncovers nearly all genetic variants linked to height.
- Silventoinen K, et al. (2016). Genetic and environmental influences on height from infancy to early adulthood. Scientific Reports, 6, 28496.
info Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. If you have concerns about your child's growth, please consult a qualified healthcare professional.