How tall will my child be? 4 prediction methods compared

The four methods at a glance

Method	What it uses	Roughly how accurate
Mid-parental height	Both parents’ heights only	Range of about ±8.5cm
Doubling height at age 2	Child’s height at age 2	Not formally validated; considered simple but inaccurate
Khamis-Roche	Child’s height, weight, age (4-17.5y) plus both parents	About ±5.3cm (boys) / ±4.3cm (girls), 90% interval
Bone-age X-ray	Hand-and-wrist X-ray, clinician-interpreted	The most accurate of the four, but requires a clinical visit

Try the calculator below, pre-filled with a worked example: a father at 5’10” (177.8cm) and mother at 5’5” (165.1cm), expecting a boy.

Father's height

Mother's height

Child's sex

BoyGirl

Estimated adult height

178 cm

Likely range 169.5 cm to 186.5 cm.

A population-level estimate (the mid-parental method), not a medical prediction. It knows nothing about this specific child's own growth.

See the predicted height on the board→

Method 1: mid-parental height

This is the method the calculator above uses. It’s also what most people mean by a quick “will my child be tall” estimate. For boys it’s (father’s height + mother’s height + 13cm) ÷ 2; for girls it’s (father’s height + mother’s height − 13cm) ÷ 2. The result is shown as a range of about ±8.5cm either side of the central figure.

It’s a long-established clinical rule of thumb, commonly attributed to Tanner and colleagues. It’s still widely used today as a first-pass estimate. Its main limitation is that it only looks at the parents. It has no information about the child’s own growth so far, their nutrition, health, or how closely they happen to track either parent.

For the worked example above — a 177.8cm father and 165.1cm mother, expecting a boy — the formula gives (177.8 + 165.1 + 13) ÷ 2 = 178.0cm. The likely range is roughly 169.5–186.5cm. That’s a wide band, which is exactly why the other three methods exist: they try to narrow it.

For a girl with the same parents, the formula subtracts 13cm instead of adding it: (177.8 + 165.1 − 13) ÷ 2 = 165.0cm. The same ±8.5cm range applies, giving roughly 156.5–173.5cm. Try either sex yourself with the calculator above; it recalculates instantly as you change the inputs.

Method 2: doubling height at age 2

A much older piece of folk wisdom holds that a child’s adult height is roughly double their height on their second birthday. It’s simple to remember and needs only one measurement, which explains its staying power.

It isn’t a formally validated method, though. Sports-science sources that catalogue height-prediction techniques describe it as simple but inaccurate, compared with regression-based methods that use more inputs. It can work as a loose, low-effort ballpark. It shouldn’t be relied on for anything specific, and it gives no sense of the uncertainty around its own guess.

Part of the problem is that it collapses a child’s future growth into a single multiplication. Growth isn’t perfectly proportional between age 2 and adulthood. Puberty timing alone can shift the final outcome by several centimetres in either direction. A method with no stated error range also gives no way to judge how far off any single guess might be.

Method 3: the Khamis-Roche method

Published by Khamis and Roche in the journal Pediatrics in 1994, this method takes a more sophisticated approach than either of the first two. Instead of relying only on the parents, or only on one childhood measurement, it combines the child’s current height, weight and age with both parents’ heights in a regression model.

It’s designed for children roughly aged 4 to 17.5 years. Because it draws on the child’s own growth trajectory rather than genetics alone, it’s generally more accurate than the mid-parental formula. Reported accuracy is around ±5.3cm for boys and ±4.3cm for girls within a 90% prediction interval. That’s narrower than the ±8.5cm mid-parental range, though still a real margin, not an exact figure.

The trade-off is that it needs more inputs than mid-parental height. It isn’t built into this site’s calculator, which uses the simpler mid-parental method instead. Several dedicated height-predictor tools online implement Khamis-Roche specifically, if you have a child’s current height and weight to hand.

Because it re-runs as the child grows, a Khamis-Roche estimate made at age 6 and again at age 12 will typically narrow further. That’s because more of the child’s own growth is on record by then. Mid-parental height, by contrast, gives the same answer at any age, since it never looks at the child at all.

Method 4: bone-age and skeletal-maturity methods

The most accurate methods available — Bayley-Pinneau, Roche-Wainer-Thissen and Tanner-Whitehouse among them — read skeletal maturity from a hand-and-wrist X-ray. Bone age can run ahead of or behind chronological age. That gap is itself informative about how much growing a child has left to do.

These methods sit firmly in the “ask a paediatrician” tier. They need imaging equipment and trained interpretation, so they’re only available through a doctor. Typically that happens when there’s a specific clinical reason to assess a child’s growth more precisely, rather than as a routine check.

Why the methods can disagree

It’s normal for these four methods to give slightly different answers for the same child. That’s not a sign that one of them is simply wrong. Each is built from different information and a different statistical model, so each has its own blind spots.

Mid-parental height ignores the child entirely, relying only on the assumption that a child tracks close to the midpoint of their parents. Doubling at age 2 ignores the parents entirely, and assumes early growth scales in a fixed ratio to adult height, which isn’t strictly true.

Khamis-Roche sits between the two, using both, but it’s still a statistical average across many children, not a certainty for one child. Bone-age methods come closest to observing the individual child directly. That’s exactly why they need a clinical X-ray rather than a formula.

Comparing all four methods

Method	Inputs needed	Typical accuracy	Where to get it
Mid-parental height	Father’s and mother’s height	±8.5cm range	This site’s child height predictor
Doubling height at age 2	Child’s height at age 2	Not formally validated; simple but inaccurate	Manual calculation, no tool needed
Khamis-Roche	Child’s height, weight, age (4-17.5y) plus both parents	~±5.3cm (boys) / ~±4.3cm (girls), 90% interval	Dedicated Khamis-Roche calculators
Bone-age X-ray	Hand-and-wrist X-ray, clinician read	Most accurate of the four	A GP or paediatrician referral

The pattern across all four is straightforward. Accuracy tends to improve as a method uses more information about the child specifically, rather than parents alone. The most accurate option requires clinical imaging rather than a calculator.

Method and sources

The mid-parental formula and its ±8.5cm range are implemented directly in this site’s child height predictor calculator, following the long-established Tanner-attributed rule of thumb. The doubling-at-age-2 method and the bone-age tier are both described, and their relative accuracy assessed, on Topend Sports’ overview of height-prediction methods, cited below.

The Khamis-Roche method itself was introduced in Khamis and Roche’s 1994 paper in Pediatrics, cited below. Its specific accuracy figures (±5.3cm for boys, ±4.3cm for girls, 90% prediction interval) are drawn from InfantChart’s summary of the method, also cited below.

None of these figures are this site’s own research. They’re compiled from the cited sources, so you can check them directly rather than take an unsourced number on trust. Where a source gives a range rather than a single figure, this article reports that range rather than picking one number out of it.

This is an estimate, not medical advice. Every method here, including the calculator on this page, gives a statistical range rather than a certainty. None of them account for a specific child’s individual health or growth history. If you have a genuine concern about a child’s growth, talk to a GP or paediatrician, who can also arrange a bone-age assessment if it’s appropriate.

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Try the child height predictor with your own numbers, or open the comparison board to see a predicted height stood next to anyone else you choose.