Tanner's formula
The genetic target height (mid-parental height) is calculated from the parents' height. Men are on average 13 cm taller than women, so for boys 13 cm is added to the sum, and for girls it is subtracted.
Example. Father 180 cm, mother 165 cm. Son: (180 + 165 + 13) / 2 = 179 cm, likely range 170.5–187.5 cm. Daughter: (180 + 165 − 13) / 2 = 166 cm, range 157.5–174.5 cm.
How accurate the prediction is
About 95% of children grow to within ±8.5 cm of their target height. The result is affected by nutrition, sleep, physical activity, chronic illness and the timing of puberty. A more precise prediction comes from assessing bone age on a hand X-ray — an endocrinologist can order one.
When to see a doctor
- Your child is noticeably shorter or taller than their peers and outside their target range.
- Growth has sharply slowed down or sped up: the child has "moved" to a different line on the growth chart.
- Signs of puberty appeared before age 8 in girls or age 9 in boys.
The prediction is approximate. A paediatrician can check whether your child's height matches their age using the WHO growth charts.