Every parent asks it at some point, usually while marking a pencil line on a door frame: how tall will my child be? There is no test that can give an exact answer, because adult height depends on genes, nutrition, sleep, general health, and the timing of puberty. What you can get — in about ten seconds — is a sensible estimate with an honest range around it. That is exactly what a height predictor calculator does.
This guide explains the method behind the calculator, shows you how to work it out by hand, gives real examples, and explains how accurate the result really is. Use the calculator at the top of this page first, then read on to understand what your number means.
The mid-parental height method, in plain language
The most widely used estimate is called mid-parental height, also known as the Tanner method. It averages the two parents' heights and then adjusts for the average height difference between adult men and women, which is about 13 cm (5 inches).
- Boys: For a boy: add the father's height and the mother's height, add 13 cm, then divide by 2.
- Girls: For a girl: add the father's height and the mother's height, subtract 13 cm, then divide by 2.
In inches, the same method works just as well: add 5 inches for a boy, subtract 5 inches for a girl, then divide by 2. The result is not a promise. It is the centre of the range your child is most likely to finish in.
Worked examples you can check by hand
| Example | Calculation | Predicted adult height | Likely range (±8.5 cm) |
|---|---|---|---|
| Boy — Dad 178 cm, Mum 165 cm | (178 + 165 + 13) ÷ 2 | 178 cm (about 5 ft 10 in) | 169.5–186.5 cm |
| Girl — Dad 178 cm, Mum 165 cm | (178 + 165 − 13) ÷ 2 | 165 cm (about 5 ft 5 in) | 156.5–173.5 cm |
| Boy — Dad 170 cm, Mum 160 cm | (170 + 160 + 13) ÷ 2 | 171.5 cm (about 5 ft 8 in) | 163–180 cm |
| Girl — Dad 185 cm, Mum 172 cm | (185 + 172 − 13) ÷ 2 | 172 cm (about 5 ft 8 in) | 163.5–180.5 cm |
Notice what the examples show: the same parents produce a prediction about 13 cm apart for a son and a daughter, and the range is wide. Two brothers with identical parents can still finish several centimetres apart, because each child inherits a different mix of genes from grandparents and earlier generations as well.
How accurate is a height predictor calculator?
About 95 out of 100 children finish within roughly 8.5 cm (about 3.3 inches) of their mid-parental height. That also means about 5 in 100 healthy children finish outside that range, simply because genetics is wider than a two-parent average. Read your result as 'most likely around here', never as 'definitely this tall'.
Accuracy is lower when a parent is much taller or shorter than their own parents, when a child has a medical condition that affects growth, or when puberty starts unusually early or late. Early puberty can make a child look tall for their age and then stop growing sooner; late puberty does the opposite. Neither pattern is automatically a problem, but both make any early prediction less reliable.
What else affects how tall a child grows?
- Genetics. Genes set the range. Height is influenced by many genes, not one, which is why children land at different points inside the family range.
- Nutrition. Regular meals with enough protein, calcium, and vitamin D support growth. Severe or long-term undernutrition can reduce final height.
- Sleep. Growth hormone is released mainly during deep sleep, so consistent sleep matters throughout childhood and the teenage years.
- Health. Thyroid problems, growth hormone deficiency, coeliac disease, and some long-term illnesses can slow growth — and many are treatable when caught early.
- Activity. Exercise supports strong bones and general health, but no sport or stretching routine can make a child taller than their genetic range.
A more precise method: Khamis-Roche
Doctors who need a tighter estimate sometimes use the Khamis-Roche method. As well as the parents' heights, it uses the child's current age, height, and weight, with tables of coefficients from research published in the journal Pediatrics in 1994. For children aged 4 to 17.5 years, about 90% of boys finished within 5.3 cm of the prediction and about 90% of girls within 4.3 cm — noticeably tighter than the mid-parental range.
Khamis-Roche has limits too. It was developed from data on white children in the United States, it needs accurate current measurements, and it should not be used for children with conditions that affect growth. Our calculator uses the mid-parental method today because it needs only two numbers and works at any age. A Khamis-Roche calculator is planned as a later addition, and it will be clearly labelled when it arrives.
When should you talk to a doctor about growth?
A prediction alone is never a reason to worry. A check-up is worth booking if your child is growing much more slowly than before, drops across percentile lines on a growth chart, is far shorter than classmates and family expectations, shows signs of very early puberty (before age 8 in girls or 9 in boys), or has no signs of puberty by age 13 in girls or 14 in boys. A doctor can measure growth over time, and that pattern over 6 to 12 months tells far more than any single calculator result.
Frequently asked questions
Can a height predictor tell me my child's exact adult height?
No. It gives the centre of a likely range. About 95% of children finish within about 8.5 cm of the mid-parental estimate, so always read the range, not just the single number.
At what age can I use this calculator?
At any age, because it uses only the parents' heights. That is its strength and its limit: it cannot adjust for how your child is actually growing, which is why growth charts and regular measurements matter as well.
My child is taller than the prediction already. Is something wrong?
Not necessarily. Children grow at different speeds, and a child who matures early may be tall now and finish near or below the prediction. If growth suddenly speeds up, slows down, or puberty starts very early, ask a doctor to review the growth pattern.
Does doubling a child's height at age 2 work?
It is a rough rule of thumb — height at age 2 is often about half of adult height — but it is less reliable than the mid-parental method and fails often enough that we do not use it in the calculator.
Can food, exercise, or supplements make my child taller than predicted?
Good nutrition and sleep help a child reach their genetic range; they do not raise the range itself. Be cautious with any product that promises extra height — no supplement has been shown to add height in a healthy, well-nourished child.
Try it now: Enter both parents' heights in the height predictor calculator at the top of this page. You will get a predicted adult height in centimetres and in feet and inches, with the likely range shown alongside it.
Disclaimer: This article and calculator are for general information only and are not medical advice. Height prediction is an estimate, not a diagnosis. If you are concerned about your child's growth, talk to your child's doctor.