Height Calculator

The mid-parental height method explained

The Predicting Based on the Parents' Heights Only calculator uses the mid-parental height method, a standard, widely published estimate that starts from the simple idea that height is strongly inherited from both parents. The formula averages the two parents' heights, then applies a fixed adjustment for the child's sex: add 13cm for a boy, or subtract 13cm for a girl, before dividing by two.

Worked example. A mother is 165cm tall and a father is 180cm tall. For a boy: (165 + 180 + 13) ÷ 2 = 358 ÷ 2 = 179.0cm predicted adult height. For a girl from the same two parents: (165 + 180 − 13) ÷ 2 = 332 ÷ 2 = 166.0cm. Notice the girl's prediction is exactly 13cm lower than the boy's, since that 13cm adjustment is the only thing that differs between the two calculations for the same parents.

Around that single predicted number, researchers also cite an expected range of about 8.5cm above and below it, roughly 3.4 inches. For the boy in the example above, that range runs from 170.5cm to 187.5cm. This range is not arbitrary padding, it is the commonly cited spread that reflects how much individual children vary even when their mid-parental estimate is identical.

Child's Adult Height Prediction: blending two independent estimates

The Child's Adult Height Prediction calculator does not replace the mid-parental method, it adds a second, independent estimate alongside it and averages the two. The second estimate starts from a different question entirely: instead of asking what the parents suggest, it asks how much of adult height a typical child of this exact age and sex has already reached, then scales the child's own current height up by that same proportion. A 6-year-old boy, for instance, has on average reached about 65.7% of his eventual adult height, so a current height is divided by 0.657 to get a second guess at his final height.

Both numbers, the mid-parental estimate and this current-growth estimate, are shown next to the averaged headline figure, specifically so the method never behaves like a black box. The percentages this second estimate relies on come from official World Health Organization growth data, and the full table plus a worked example is in How Tall Will I Be? Predicting Adult Height Explained.

A note on both tools: these estimates are based on population growth averages and show typical patterns only. Individual children vary substantially in growth timing and tempo, especially around puberty. Neither is a diagnosis or a substitute for a pediatrician's assessment, particularly if a child's growth seems unusually fast, slow, or off-pattern for their family history.

Genetics and why height runs in families

Twin and family studies consistently put the heritability of adult height somewhere around 60-80%, meaning that share of the height differences between people in a population is statistically associated with genetic differences between them. Height is not controlled by one gene, it is polygenic: hundreds of genes, each with a small effect, add up to a person's genetic potential. That is a large part of why siblings with the same two parents can still end up noticeably different heights from each other, and from a mid-parental estimate that only sees the parents' own two numbers.

There is a second, statistical effect worth knowing about, called regression to the mean: on average, the children of unusually tall parents tend to land somewhat closer to the population average than their parents are, and the same is true in the other direction for unusually short parents. This is not a weakening of genetics, it is what happens whenever a trait is influenced by many independent factors rather than one: extreme combinations of those factors are rarer in the next generation simply by chance. The idea was named by the Victorian scientist Francis Galton, who first described it in the 1880s while studying exactly this: how parents' heights related to their children's.

How height changes with age

Growth is not a straight line. Infancy is by far the fastest period of postnatal growth, with a typical baby gaining roughly 25cm (about 10 inches) of height in the first year alone. Growth then settles into a much steadier pace through early and middle childhood, typically around 5-7cm a year, a period where the current-growth half of Child's Adult Height Prediction tends to track closest to the eventual mid-parental figure.

Puberty brings the next major shift: a growth spurt that, at its peak, can add 8-12cm in a single year. Girls typically enter this spurt earlier, often around 10-12 years old, while boys typically enter it a little later, often around 12-14, but sustain it longer and reach a higher peak rate, which is a large part of why the average adult height gap between men and women exists at all. Growth slows sharply once the growth plates, the cartilage regions near the ends of the long bones, fuse and close, typically by around 14-16 in girls and 16-18 in boys, after which no further height gain is possible by any natural means.

One old rule of thumb happens to line up well with the modern data this calculator uses: the folk method of doubling a boy's height at age 2, or a girl's height at 18 months, to estimate adult height. According to the WHO growth data behind Child's Adult Height Prediction, a 2-year-old boy has on average reached about 49.7% of his adult height, and an 18-month-old girl about 49.2% of hers, both close enough to the halfway point that doubling gives a rough but genuinely reasonable estimate, which is presumably why the old rule persisted for so long.

How height calculator methods for adult height prediction compare

The two prediction tools on this page sit inside a wider set of methods clinicians and researchers use, each trading off simplicity against accuracy:

• Bone-age methods (Greulich-Pyle). A hand and wrist X-ray is compared against a reference atlas (Greulich WW, Pyle SI, Radiographic Atlas of Skeletal Development of the Hand and Wrist, 1959) to read off a child's bone age, which can run ahead of or behind their calendar age. Remaining growth is then projected from population tables built around bone age rather than birthdate. This is the actual basis of the Bayley-Pinneau method some other sites reference, which needs an X-ray and is not something a birthdate-only calculator can reproduce.
• Khamis-Roche. A statistically calibrated method (Khamis HJ, Roche AF, "Predicting adult stature without using skeletal age: the Khamis-Roche method," Pediatrics, 1994) that combines a child's current height, weight, age and mid-parental height, without needing an X-ray. It was built from the long-running Fels Longitudinal Study and is generally considered one of the more accurate non-X-ray methods for children roughly 4 to 17 years old. This page does not implement Khamis-Roche; Child's Adult Height Prediction above is a simpler, fully transparent average of two estimates rather than a calibrated regression model.
• CDC growth charts. Rather than predicting a single adult height, these track a child's height percentile against a large reference population over repeat visits. A child holding a steady percentile over time is the reassuring pattern pediatricians actually look for; a percentile that suddenly shifts is what prompts a closer look, regardless of what any calculator predicts.
• Simple methods. The mid-parental formula and the current-height-trajectory estimate this page uses both fall in this category: quick, transparent, and reasonable as a starting estimate, but built from far less information than a bone-age reading or a calibrated multi-variable model.

How to get taller

Genetics sets the range a person can grow into; nutrition, activity, sleep and general health during childhood and adolescence decide how close to the top of that range a person actually lands. None of the four below can push someone past their genetic ceiling, but each can matter while the growth plates are still open:

• Nutrition. Adequate protein, calories, calcium, vitamin D and zinc during the growing years support normal bone growth. This is not theoretical: population-level height has measurably increased over successive generations in many countries as nutrition and childhood health improved, a well-documented pattern researchers call the secular trend in height. Chronic malnutrition or untreated illness in childhood, conversely, can permanently reduce final adult height.
• Exercise. Regular physical activity supports healthy bone density and normal growth-plate development during the growing years. There is no good evidence that exercise itself adds height beyond a person's genetic potential, but it supports the general health that growth depends on.
• Sleep. Growth hormone is released mainly during deep sleep, so consistent, adequate sleep through childhood and the teenage growth spurt is part of supporting a normal growth trajectory.
• Posture. Worth being precise about: good posture does not add height, it just stops slouching from making someone look shorter than they actually are by straightening out the spine's natural curve. It can change a measured height by a small margin depending on how someone is standing at the moment they are measured, but it does not lengthen bones.

Once the growth plates fuse after puberty, height is fixed. No diet, exercise, stretching routine or product can add height in adulthood, whatever the growth plates allowed up to that point is the final number.

What these methods do not capture

Parental height and a child's own current growth are both strong signals, but it is honest to be upfront about what neither tool on this page can see:

• Both only explain part of the picture. Height is influenced by many genes beyond the two visible parental heights, so two siblings with the same parents can still end up noticeably different heights from each other and from either predicted number.
• Nutrition and health during growth matter. A child's diet, general health, sleep and any chronic conditions during childhood and adolescence can all shift final adult height away from either a purely genetic estimate or a purely current-growth one.
• The mid-parental range is a real uncertainty, not a formality. Most children measured against that method end up somewhere inside its ±8.5cm range rather than exactly on the single predicted number each calculator on this page shows.
• Both are one-time estimates, not ongoing monitoring. For a specific medical concern about how a child is growing, a pediatrician tracking height on a proper growth chart over several visits is far more reliable than any single calculation done at one point in time.