Height Calculator

About This Tool

Predicting a child's adult height has fascinated parents and pediatricians for centuries, and the mid-parental height method remains one of the simplest and most widely used approaches. While no formula can predict adult height with perfect accuracy — genetics, nutrition, health conditions, and environmental factors all play a role — the mid-parental method provides a reasonable estimate that is accurate within about 2 inches for the majority of children.

The mid-parental height formula works on the principle that children inherit height potential from both parents, with an adjustment for the average height difference between males and females (approximately 5 inches or 13 cm). The method assumes that height is a polygenic trait — influenced by hundreds of genetic variants — and that the average of both parents' genetic contributions provides a reasonable prediction of the child's adult stature.

How the Mid-Parental Method Works

For boys, the formula adds 5 inches (13 cm) to the mother's height before averaging with the father's height. This accounts for the fact that males are on average taller than females. For girls, 5 inches is subtracted from the father's height before averaging with the mother's height. The result is the predicted adult height, with a typical range of plus or minus 2 inches (5 cm) encompassing about 95% of cases. Some versions of the formula use a ±4 inch range for a wider confidence interval.

Accuracy and Limitations

Research shows that the mid-parental method correlates reasonably well with actual adult height, with a correlation coefficient of about 0.7. However, it has notable limitations. It assumes average nutrition, health, and environmental conditions. Children who experience chronic illness, malnutrition, hormonal disorders, or severe psychological stress during growth periods may not reach their predicted height. Conversely, children in environments with better nutrition than their parents had may exceed the prediction. The formula also does not account for regression to the mean — very tall parents tend to have children who are tall but somewhat shorter than predicted, and very short parents tend to have children slightly taller than predicted.

Factors That Influence Adult Height

Genetics account for roughly 60-80% of height variation, with the remaining 20-40% influenced by environmental factors. Nutrition is the most significant non-genetic factor — adequate protein, calcium, vitamin D, and zinc during childhood and adolescence are essential for reaching genetic height potential. Growth hormone levels, thyroid function, and pubertal timing also play important roles. Children who enter puberty earlier tend to have an earlier growth spurt but may end up slightly shorter as adults because their growth plates close sooner. Chronic conditions like celiac disease, growth hormone deficiency, and Turner syndrome can significantly impact final height if untreated.

Growth Patterns by Age

Infants typically grow 10 inches (25 cm) in their first year. Growth slows to about 2.5 inches (6 cm) per year from age 2 until puberty. During puberty, a growth spurt adds 3-4 inches per year for girls (peaking around age 12) and 4-5 inches per year for boys (peaking around age 14). Girls generally reach their adult height by age 14-16, while boys continue growing until age 16-18, with some adding height through age 20. Pediatricians track growth using standardized CDC or WHO growth charts, where a child's height percentile relative to age and sex is more meaningful than absolute height at any single point.

When to Consult a Doctor

Parents should consult a pediatric endocrinologist if their child's height consistently falls below the 3rd percentile, if growth rate drops below 2 inches per year after age 3, if height deviates significantly from the mid-parental prediction (more than 4 inches below), or if puberty starts unusually early (before age 8 in girls or 9 in boys) or late (after age 13 in girls or 14 in boys). A bone age X-ray of the left hand can help assess remaining growth potential by showing how mature the growth plates are compared to chronological age. Growth hormone testing may be recommended if growth hormone deficiency is suspected.