Height Calculator Guide: How to Predict Adult Height (2026)

How Height Prediction Works

Predicting how tall a child will be as an adult has fascinated parents and doctors for centuries. Modern methods range from simple parental height formulas to sophisticated bone age analysis. None are perfect, but they can narrow the range considerably.

Height is a polygenic trait — hundreds of genes contribute small effects. A landmark 2022 study in Nature identified over 12,000 genetic variants associated with height, collectively explaining about 40% of the variation in adult stature. But genes only set the ceiling. Nutrition, sleep, chronic illness, and hormonal factors determine where within that genetic range a person actually lands.

The Mid-Parental Height Formula

The most widely used prediction method in pediatric clinics is the Tanner mid-parental height formula:

• Boys: (Mother's height + Father's height + 5 inches) ÷ 2
• Girls: (Mother's height + Father's height − 5 inches) ÷ 2

The 5-inch (13 cm) adjustment accounts for the average height difference between adult males and females. This formula predicts adult height within a range of about ±2 inches (5 cm) for roughly 95% of children.

Worked Example

Father is 5'10" (70 inches), mother is 5'4" (64 inches). Predicting their son's adult height:

• (64 + 70 + 5) ÷ 2 = 139 ÷ 2 = 69.5 inches (5'9.5")
• Expected range: 67.5" to 71.5" (5'7.5" to 5'11.5")

Growth Charts and Percentiles

The CDC and WHO publish growth charts that plot height-for-age percentiles based on large population studies. A child tracking the 75th percentile at age 5 is likely to remain near that percentile through adolescence, barring illness or nutritional changes.

Pediatricians watch for children who “cross percentile lines” — a child dropping from the 60th to the 20th percentile over a year warrants investigation. The Khamis-Roche method uses current height, weight, and parental heights to predict adult stature, and has been validated as one of the more accurate non-clinical methods.

Bone Age and the Greulich-Pyle Method

For clinical accuracy, doctors use a bone age X-ray of the left hand and wrist. The Greulich-Pyle atlas (updated 2020) compares a child's skeletal maturity to reference images. Combined with the Bayley-Pinneau tables, bone age predicts adult height within about 1 inch for children over age 7.

A child whose bone age is younger than their chronological age typically has more growth remaining. This is common in children with constitutional growth delay — “late bloomers” who hit puberty later but often reach normal adult height.

When Children Stop Growing

Growth plates (epiphyseal plates) are areas of cartilage near the ends of long bones. Estrogen triggers their fusion, which is why puberty timing matters so much:

• Girls: Peak growth velocity occurs about 1 year before the first period (menarche), typically around age 11–12. Most girls grow only 1–3 inches after menarche and reach final height by 14–16.
• Boys: Peak growth velocity occurs around age 13–14, with most boys reaching final height by 16–18. Late bloomers may continue growing into their early 20s.

Factors That Influence Final Height

Nutrition

Protein intake during childhood is the single most important nutritional factor for growth. The secular trend in height — the fact that average heights increased 3–4 inches globally over the 20th century — is largely attributed to improved nutrition, particularly protein and dairy consumption. Deficiencies in zinc, vitamin D, and calcium can also limit growth.

Sleep and Growth Hormone

Growth hormone (GH) is secreted in pulses during deep sleep, with the largest pulse occurring in the first 1–2 hours of sleep. Children who consistently get inadequate sleep may have reduced GH secretion. The American Academy of Pediatrics recommends 9–12 hours for ages 6–12 and 8–10 hours for teenagers.

Chronic Illness

Conditions like celiac disease, inflammatory bowel disease, chronic kidney disease, and untreated hypothyroidism can significantly reduce growth velocity. In many cases, treating the underlying condition allows “catch-up growth” if growth plates haven't yet fused.

Early or Late Puberty

Early puberty (precocious puberty) can lead to shorter adult height because growth plates fuse sooner, despite an initial growth spurt. Conversely, delayed puberty often results in taller adult height because bones have more time to grow before the plates close.

Frequently Asked Questions

How accurate is the mid-parental height formula?

The mid-parental height formula predicts adult height within about 2 inches (5 cm) for most children — roughly a 4-inch range. It accounts for about 40–60% of the genetic contribution to height. Growth charts combined with bone age X-rays improve accuracy to within 1 inch for children over age 7.

What is the mid-parental height formula?

For boys: (mother's height + father's height + 5 inches) ÷ 2. For girls: (mother's height + father's height − 5 inches) ÷ 2. The 5-inch (13 cm) adjustment accounts for the average height difference between males and females. This formula was developed by Tanner and is still widely used in pediatric practice.

At what age do children stop growing?

Most girls reach their final adult height by age 14–16, approximately 2 years after their first menstrual period. Most boys reach their final height by age 16–18. Growth plates in the long bones fuse under the influence of estrogen, which is why earlier puberty generally leads to shorter adult height.

Can nutrition affect a child's final height?

Yes. While genetics determine about 60–80% of adult height, nutrition plays a significant role — especially protein intake during childhood. Chronic malnutrition can reduce final height by several inches. Conversely, improved nutrition is why average heights have increased 3–4 inches globally over the past century.

What is a bone age X-ray and how does it predict height?

A bone age X-ray (usually of the left hand and wrist) compares a child's skeletal maturity to standard references. If bone age is delayed compared to chronological age, the child likely has more growing time remaining. The Greulich-Pyle and Bayley-Pinneau methods use bone age to predict final height with better accuracy than parental height formulas alone.