Child Height Predictor

A hundred and seventy-four centimetres, give or take eight and a half

A boy with a mother of 160 cm and a father of 175 cm has a predicted adult height of 174.0 cm, with a likely range of 165.5 to 182.5 cm.

That range is the honest part of the answer. The prediction is a midpoint, and the plus or minus 8.5 cm on either side is not a caveat to be ignored — it spans 17 centimetres, which is the difference between noticeably short and noticeably tall.

The mid-parental height method

The standard clinical estimate, sometimes called the Tanner method:

For a boy: (mother's height + father's height + 13) ÷ 2 (160 + 175 + 13) ÷ 2 = 348 ÷ 2 = 174.0 cm

For a girl: (mother's height + father's height − 13) ÷ 2

The 13 cm adjustment approximates the average adult height difference between men and women. The result is the mid-parental height — the centre of the range a child's genetics would be expected to produce.

The conventional confidence interval is about ±8.5 cm, which captures roughly 95% of outcomes for children of those parents.

What the prediction does and does not capture

Adult height is roughly 80% heritable, which is why parental height predicts as well as it does. The remaining variation comes from factors the formula cannot see:

Nutrition, particularly in the first two years and during the adolescent growth spurt. This is the largest modifiable factor, and population-level height increases across generations are largely attributable to it. Adequate protein, calories and micronutrients matter considerably.

Childhood illness, especially recurrent infection or chronic conditions affecting absorption.

Sleep, during which most growth hormone is secreted.

Endocrine conditions — growth hormone deficiency, hypothyroidism, precocious or delayed puberty — all of which can move final height substantially and several of which are treatable if identified early.

Timing of puberty, which determines how long growth continues before the growth plates close.

Note the generational effect this produces: children frequently exceed the mid-parental prediction where nutrition has improved between generations, which has been a consistent pattern in India over recent decades.

When growth stops

Growth ends when the epiphyseal growth plates fuse, typically around 14 to 16 for girls and 16 to 18 for boys, though with wide individual variation. Most of the final height is gained in the pubertal growth spurt, which occurs earlier in girls.

A bone age X-ray of the left hand and wrist gives a considerably more accurate prediction than parental height, because it shows how much growth potential remains rather than estimating from genetics alone. This is what a paediatric endocrinologist would use where height is a genuine clinical concern.

When to seek advice

The prediction here is for interest. Growth becomes a clinical question in specific circumstances, and these are worth knowing:

Crossing percentile lines. A child tracking steadily along the 25th percentile is growing normally. One who drops from the 50th to the 10th over a year is not, regardless of absolute height — the trajectory matters far more than the position.

Height significantly below the mid-parental range, particularly more than the ±8.5 cm band would explain.

A markedly slow growth rate, generally under about 4–5 cm a year in mid-childhood.

Very early or very delayed puberty.

In all of these, a paediatrician rather than a calculator is the right next step. This is a general estimate and is not medical advice.

Common mistakes

Reading the midpoint as a prediction. The range is 17 cm wide.

Applying the boy's formula to a girl. The adjustment reverses.

Ignoring the growth trajectory. Percentile crossing matters more than a single measurement.

Assuming nutrition cannot change the outcome. It is the largest modifiable factor.

Delaying advice when growth is genuinely slow. Several causes are treatable, and treatment works best before the growth plates close.