About the Child Height Predictor
This child height predictor estimates how tall a son or daughter is likely to be as an adult. Enter both biological parents’ heights and the child’s sex, and it calculates the mid-parental target height used by paediatricians, along with Tanner’s ±8.5 cm range, which spans roughly the 3rd to 97th percentile of expected adult height. If you know your child’s height at age 2 (boys) or 18 months (girls), add it for a second estimate using the classic doubling rule, and the calculator averages the two.
Height is strongly inherited, which is why the parents’ average — adjusted by 13 cm (about 5 inches) for the average difference between men and women — is the standard starting point. Paediatric endocrinologists use this target height to judge whether a child’s growth is tracking as expected on a growth chart.
Predictions are estimates, not guarantees. Nutrition, health, sleep and the timing of puberty all affect final height, and the actual result can reasonably fall anywhere in the range shown. Concerns about growth should always be discussed with your child’s doctor.
How to use the child height predictor
- 1Choose your child’s sex and your preferred units.
- 2Enter the biological mother’s and father’s heights.
- 3Optionally enter the child’s height at age 2 (boys) or 18 months (girls).
- 4Read the predicted adult height and the likely range.
Formula and method
The mid-parental height method (Tanner) averages the two parents’ heights after adjusting for sex: 13 cm (about 5 inches) is added for a boy or subtracted for a girl, the average height difference between adult men and women. Tanner and colleagues (1970) gave the target a range of ±8.5 cm (±3.3 inches), roughly the 3rd to 97th percentile, reflecting the spread of adult heights among children of the same parents. Recent reviews note the formula tends to underestimate adult height for children of very short parents.
This calculator adds 13 cm for the sex difference, as in Tanner’s original formula; populations with a different average male–female gap may differ slightly.
The doubling rule is an older rule of thumb: boys reach about half their adult height at age 2 and girls at about 18 months, so doubling that height gives a second estimate. When you enter a toddler height the calculator averages the two methods; otherwise it reports the mid-parental target.
- mother, father
- Biological parents’ adult heights
- 13 cm
- Average adult height difference between men and women
- ± 8.5 cm
- Tanner range around the target (≈3rd–97th percentile)
Worked examples
Boy, parents 165 cm and 178 cm
Adding 13 cm to the parents’ total (165 + 178 = 343) gives 356, and halving it gives 178 cm (about 5′10″). Most boys with these parents end up between 169.5 and 186.5 cm.
Girl, parents 5′4″ and 5′10″ (inches)
The parents are 162.56 cm and 177.8 cm. Subtracting 13 cm and halving gives (340.36 − 13) ÷ 2 = 163.7 cm, or about 64.4 inches — roughly 5′4″.
Boy measured 88 cm at age 2
Doubling the 88 cm height at age 2 gives 176 cm, close to the 178 cm mid-parental target. Averaging the two methods predicts about 177 cm.
Frequently asked questions
How accurate is a child height predictor?+
The mid-parental method gives a target with a range of about ±8.5 cm (3.3 inches), roughly the 3rd to 97th percentile of expected adult height, so most children land within it. Methods that add a bone-age X-ray, used by paediatric endocrinologists, can be more precise.
Does the doubling height at age 2 rule work?+
It is a rough rule of thumb: boys are typically about 49–50% of adult height at 24 months and girls around 18 months. It works reasonably for many children but can be several centimetres off, especially with early or late puberty.
Which parent determines height?+
Both parents contribute roughly equally. Height is highly heritable — around 80% of the variation between people is genetic — which is why the calculation uses the average of both parents’ heights.
Can nutrition and sleep make my child taller?+
Good nutrition, adequate sleep and treating chronic illness help a child reach their genetic potential, but they do not push height far beyond it. Poor nutrition or illness, however, can reduce final height.
When do children stop growing?+
Most girls reach adult height around 14–15 years, a couple of years after their first period, and most boys around 16–18 years, once the growth plates close after puberty.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.