Child Height Predictor Calculator
How tall will a child grow? One widely taught estimate is the mid-parental height method, which predicts adult height from the average of the parents' heights, adjusted up for boys or down for girls by 6.5 centimetres. This calculator applies that formula and shows the predicted height in centimetres and inches, along with the expected range of plus or minus 8.5 centimetres that captures most outcomes. It is an educational estimate only: genetics, nutrition, and health all matter, and any real concern about growth belongs with a paediatrician.
Mid-parental height formula
Boy: predicted = (father + mother + 13) / 2
Girl: predicted = (father + mother - 13) / 2
Range low = predicted - 8.5 cm
Range high = predicted + 8.5 cm
Inches = centimetres / 2.54
The 13 centimetres is the average adult height difference between men and women, split as a plus or minus 6.5 centimetre adjustment to the parental average. The plus or minus 8.5 centimetre band is the usual expected range around the target.
Growth context
- The method, attributed to Tanner, is a simple estimate, not a precise forecast.
- Most children fall within about plus or minus 8.5 centimetres of the mid-parental target.
- The 13 centimetre sex adjustment reflects average adult male-female height difference.
- Nutrition, health, hormones, and genetics beyond parental height all affect final stature.
- Paediatricians track growth on official charts over time; consult one with any concerns.
Child height predictor: frequently asked questions
What is the mid-parental height method?
The mid-parental height method, often credited to Tanner, estimates a child's likely adult height from the average of the parents' heights, adjusted for the child's sex. For a boy it adds 6.5 centimetres to the parental average; for a girl it subtracts 6.5 centimetres. The result is a midpoint, with an expected range around it.
What is the formula in detail?
Take the mother's and father's heights in centimetres. For a boy, the target is (father plus mother plus 13) divided by 2. For a girl, it is (father plus mother minus 13) divided by 2. The 13 centimetres reflects the average adult height difference between men and women.
How accurate is the prediction?
It is an estimate, not a guarantee. The method gives a target with an expected range of roughly plus or minus 8.5 centimetres (about 3.3 inches) around it, within which most children fall. Genetics, nutrition, health, and other factors all influence final height, so individual outcomes vary.
Why does sex change the result?
Adult men are on average taller than adult women by roughly 13 centimetres. The method adjusts the parental average up for boys and down for girls by half that difference, 6.5 centimetres, so the predicted height reflects the typical sex-based difference in adult stature.
Should I rely on this for medical decisions?
No. This is an educational estimate based on a simple formula. Concerns about a child's growth should be discussed with a paediatrician, who can plot measurements on official growth charts over time and assess factors this calculator cannot, such as growth velocity, bone age, and overall health.
Official sources
- U.S. Centers for Disease Control and Prevention: Growth Charts.
- U.S. National Library of Medicine, MedlinePlus: Normal growth and development.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.