Child Height Predictor
Estimated adult height from parental heights
The mid-parental height method
This is the most widely used estimate, and it is straightforward:
Girls: (mother's height + father's height − 5 inches) ÷ 2
The 5-inch adjustment reflects the average adult height difference between men and women. In metric, the equivalent adjustment is 13 cm.
Worked example: a mother of 64 inches and a father of 70 inches. For a boy: (64 + 70 + 5) ÷ 2 = 69.5 inches, or about 5 ft 9½. For a girl: (64 + 70 − 5) ÷ 2 = 64.5 inches, or about 5 ft 4½.
How accurate this actually is
Honestly? Roughly. The method carries a margin of about ±4 inches (10 cm), which is wide enough that the prediction spans most of the normal adult range.
That is why this calculator shows a range rather than a single figure. A prediction of 69.5 inches really means somewhere between about 65.5 and 73.5 inches — useful for setting expectations, not for planning anything.
Height is highly heritable, with genetics accounting for roughly 80% of the variation between people. But it is polygenic, influenced by hundreds of genes, so children regularly fall outside the range their parents suggest. Tall parents sometimes have average children and vice versa — a statistical tendency known as regression to the mean.
What else influences adult height
Nutrition across childhood is the largest non-genetic factor, particularly adequate protein, calcium, and overall energy during growth periods. This is why average heights have risen substantially in many countries over the past century.
Sleep matters because growth hormone is released predominantly during deep sleep. Chronic significant sleep deprivation across childhood can affect growth.
General health — chronic illness, untreated coeliac disease, poorly controlled asthma, and hormonal conditions can all restrict growth, which is one reason growth is monitored at routine checks.
Timing of puberty affects final height in a way that surprises people. Early puberty means an earlier growth spurt but also earlier fusion of the growth plates, which can result in a shorter final height despite being tall as a child.
Growth patterns to expect
Growth is not steady. Broad expectations:
- Year 1: around 10 inches — the fastest growth of life outside the womb
- Year 2: around 5 inches
- Ages 3 to puberty: roughly 2 to 2.5 inches a year, fairly steady
- Puberty: girls typically grow 3 to 3.5 inches a year at peak, usually between 10 and 14; boys 3.5 to 4 inches a year, usually between 12 and 16
Girls typically reach adult height around 14 to 16, boys around 16 to 18, though some boys continue growing into their early twenties. After the growth plates fuse, height is fixed.
A more useful measure than any prediction
What paediatricians actually track is whether a child is following their own growth curve consistently, not whether they match a predicted number.
A child steadily on the 20th percentile is growing normally. A child dropping from the 60th to the 20th over two years is the one worth investigating — and that pattern is visible on a growth chart long before any height prediction becomes relevant.
Speak to your GP or paediatrician if your child's growth rate slows noticeably, if they cross downward through percentile lines, if they are much shorter or taller than would be expected from family history, or if puberty seems unusually early or late. Most of the time these have benign explanations, and the ones that do not are considerably easier to address before growth plates fuse.
Common Questions
How accurate is the mid-parental height method?
It carries a margin of roughly plus or minus 4 inches, which is wide. It is useful for setting rough expectations rather than for any prediction you would rely on.
Can nutrition change my child's adult height?
Yes, within genetic limits. Adequate nutrition across childhood is the largest non-genetic factor, which is why average heights have risen substantially in many countries over the past century.
Why do tall parents sometimes have shorter children?
Height is polygenic, influenced by hundreds of genes, and children tend to fall closer to the population average than their parents - a statistical pattern known as regression to the mean.
When do children stop growing?
Girls typically reach adult height around 14 to 16 and boys around 16 to 18, though some boys continue into their early twenties. Growth stops once the growth plates fuse.