data5 min readMarch 20, 2026

Adult Height Prediction: How Genetics and Growth Charts Work

The Dutch went from an average height of 5'5” in the 1860s to over 6'0” today — the tallest nation on Earth. That's a 7-inch gain in 150 years, driven almost entirely by better nutrition and healthcare. Yet within any population, the tallest and shortest people usually have tall and short parents. So which is it — genes or environment?

The 80/20 split: genetics vs environment

Studies on twins and adopted children consistently show that adult height is roughly 80% genetic and 20% environmental. The genetic component involves hundreds of genes, each contributing a tiny amount. The environmental component is mostly nutrition during childhood and adolescence, plus factors like chronic illness and sleep quality.

This means that if both parents are tall, the child will very likely be tall — but the exact height depends on whether they got adequate nutrition during their growth years. A child with tall parents who is chronically malnourished will end up shorter than their genetic potential.

The mid-parent formula

The simplest and most widely used height prediction method is the mid-parent formula (also called the Galton method, after Sir Francis Galton who developed it in the 1880s). It averages the parents' heights and adjusts for the child's sex.

Mid-Parent Height Formula:

For boys:
  predicted = (father_height + mother_height + 5 in) ÷ 2
  predicted = (father_height + mother_height + 13 cm) ÷ 2

For girls:
  predicted = (father_height + mother_height - 5 in) ÷ 2
  predicted = (father_height + mother_height - 13 cm) ÷ 2

Example (boy):
  Father: 5'10" (178 cm)
  Mother: 5'4"  (163 cm)

  predicted = (178 + 163 + 13) ÷ 2
  predicted = 354 ÷ 2
  predicted = 177 cm (5'9.7")

Accuracy: ±2 inches (±5 cm) for most cases.

Why ±2 inches? The mid-parent formula predicts the average expected height, but height follows a bell curve. About 68% of children will fall within 2 inches of the prediction. The remaining 32% will be shorter or taller, sometimes significantly so. It's a useful estimate, not a guarantee.

Growth charts and percentiles

Pediatricians use CDC growth charts (in the US) or WHO growth standards (internationally) to track a child's growth over time. These charts show percentile lines — a child at the 75th percentile is taller than 75% of children the same age and sex.

Percentile tracking — Children tend to follow their percentile line. A child at the 60th percentile at age 5 will likely be near the 60th percentile as an adult.
Crossing percentiles — Sudden jumps or drops (crossing two or more percentile lines) can signal nutritional problems, hormonal issues, or growth disorders.
Growth spurts — Puberty causes a temporary spike in growth velocity. Girls typically peak around age 11–12, boys around 13–14.

Bone age vs chronological age

A child's bone age can differ from their actual age by 1–2 years. Bone age is determined by X-raying the left hand and wrist and comparing the growth plates to a standard atlas (the Greulich-Pyle method). A child with “advanced bone age” may stop growing earlier; one with “delayed bone age” may have more growing time left.

When growth stops

Growth ends when the epiphyseal plates (growth plates) at the ends of long bones fuse shut. This happens through a process driven by sex hormones during puberty:

Milestone	Girls	Boys
Puberty onset	8–13 years	9–14 years
Peak growth velocity	~11–12 years	~13–14 years
Growth plate closure	14–16 years	16–18 years
Final adult height	~15–17 years	~17–20 years

The secular trend: why humans keep getting taller

Over the past 150 years, average human height has increased dramatically in developed nations. This is called the secular trend. It's not genetic evolution (150 years is far too short for that) — it's environmental improvement.

Netherlands — Average male height went from 165 cm (5'5”) in 1860 to 183 cm (6'0”) today, an 18 cm gain.
South Korea — Average female height increased by 8 cm in just 50 years (1960s to 2010s), one of the fastest gains ever recorded.
United States — Height gains have plateaued since the 1980s, suggesting Americans have largely reached their genetic potential.

The drivers are better childhood nutrition, reduced infectious disease, improved sanitation, and access to healthcare. Populations that are still gaining height tend to be in countries where these factors are still improving.

Your genes set the upper bound for your height. Your childhood environment determines how close you get to that ceiling. The mid-parent formula gives a useful estimate, but real prediction requires knowing the full story — genetics, nutrition, health, and timing.