Child Adult Height Predictor

How tall will my child be as an adult?

The mid-parental height formula gives a useful central estimate:

• BOY adult height = (mother + father + 13 cm) ÷ 2
• GIRL adult height = (mother + father − 13 cm) ÷ 2

The 13 cm reflects the worldwide average adult sex difference. The 95% prediction interval is roughly ±8.5 cm (about ±3.3 inches). Adult height is determined by hundreds of genes plus environmental factors — treat the calculator number as an estimate, not a prediction.

When do children stop growing?

• Girls: most height gain done by 14-15 years; essentially complete by 16-17 (epiphyses fuse).
• Boys: most height gain done by 16-17; essentially complete by 18-19. Some gain another inch or two in early 20s.

Typical growth pattern:

• Birth to 1 year: ~25 cm gain.
• Year 2: ~12 cm.
• Year 3: ~8 cm.
• Years 3 to puberty: ~5-6 cm/year.
• Pubertal growth spurt: ~8-10 cm/year (briefer, more intense).

What affects how tall a child becomes?

• Genetics — 70-80% of height variation. Both parents contribute.
• Ethnicity — population averages differ.
• Nutrition — chronic undernutrition limits growth. Average global adult height has risen 8-10 cm in 100 years from better nutrition.
• Sleep — growth hormone released mainly during deep sleep.
• Chronic disease — coeliac, IBD, cystic fibrosis, thyroid, asthma can stunt growth.
• Hormonal — growth hormone, thyroid, sex hormones.
• Illness during growth periods.

Can I make my child taller?

Mostly no — genetics dominate. But you can avoid making them shorter than their genetic potential by:

• Adequate nutrition (protein, calcium, vitamin D, zinc).
• Good sleep (preschool 11-13 hrs; school 9-12 hrs; teens 8-10 hrs).
• Regular exercise — especially weight-bearing (running, jumping, sports).
• Treating chronic illness promptly (coeliac, thyroid, asthma).

What doesn’t work: “height-increasing” supplements, hanging from bars, posture exercises beyond skeletal maturity, special diets in already-well-nourished children.

When should I worry about my child's height?

Three patterns warrant paediatric review:

• Height crossing two major centile lines (75th to below 25th, or 25th to above 75th) over a year or two.
• Persistent height below 3rd centile OR above 97th.
• Growth velocity less than expected for age (~5 cm/year between ages 3 and puberty) over 6-12 months.

Also: significant difference between siblings raised in same household; signs of precocious or delayed puberty; very late pubertal spurt; family history of growth disorders.

Different scenarios — common questions

Scenario 1: Mum 162 cm, dad 178 cm; daughter at 5 years on 50th centile

Mid-parental prediction for girl: (162 + 178 − 13) ÷ 2 = 163.5 cm. 95% interval 155-172 cm. Tracking 50th at age 5 fits this projection — trajectory looks normal.

Scenario 2: Both parents 175-180 cm; son tracking 5th centile at age 6

Mid-parental prediction for boy: ~184 cm. But son is at 5th centile (well below expected). Paediatric review. Workup: thyroid function, coeliac screen, possibly growth hormone investigation. Don’t dismiss as “just small”.

Scenario 3: 7-year-old girl starting breast development and pubic hair

Precocious puberty (girls < 8). Same-week paediatric referral. Investigation: bone-age X-ray, hormone levels, sometimes pelvic ultrasound, brain MRI in some cases. Treatable with GnRH analogues to preserve adult height.

Scenario 4: 14-year-old boy, no testicular enlargement yet

Delayed puberty (boys > 14 without sign). Often constitutional delay especially if family pattern (dad / brothers also late). Worth endocrinology referral if no progress by 14.5-15. Sometimes treated with short course of testosterone to kickstart puberty.

Scenario 5: Child treated for coeliac at age 4, growth crossed up two centile lines after gluten-free diet

Classic catch-up growth pattern. Growth was being stunted by undiagnosed coeliac. After gluten removal, normal growth resumes and child “catches up” toward their genetic trajectory. Usually plateaus on appropriate centile within 1-2 years.

Care guidance — supporting healthy growth

• Balanced Mediterranean-style diet from weaning onwards.
• Adequate protein — eggs, dairy, meat / fish, beans / lentils with most meals.
• Calcium and vitamin D — dairy, leafy greens, fortified foods. Vit D supplement (10 mcg/day) is NHS standard for UK children.
• Iron-rich foods — important throughout childhood, especially weaning and adolescence.
• Sleep — consistent bedtime, age-appropriate hours.
• Active lifestyle — 60+ minutes/day for school-age children.
• Routine paediatric visits — growth plotted at well-child visits.
• Treat illness — chronic conditions (coeliac, thyroid, asthma) impact growth.
• Mental health — severe stress can affect growth via cortisol.
• Don’t restrict diet based on height concerns — never the answer.

Limitations of this calculator

• 95% prediction interval ±8.5 cm — many children will be taller or shorter than predicted.
• Doesn’t account for chronic illness, nutritional issues, endocrine disorders.
• Less accurate for very tall or very short parents (regression to mean).
• Paediatric endocrinologists use bone-age X-rays + growth velocity for more accurate projection.
• Educational tool — not a clinical assessment.

Sources

• Tanner JM. Growth at Adolescence. Blackwell Scientific 1962.
• Khamis HJ, Roche AF. Predicting adult stature without using skeletal age. Pediatrics 1994.
• Cole TJ. Secular trends in growth. Proc Nutr Soc 2000.
• NICE NG43. Suspected developmental delay.
• NHS Growth Reference. UK-WHO growth charts.
• CDC. Clinical Growth Charts. 2000.