Child Growth Predictor - Adult Height Forecast from Parent Heights

The problem: you have no idea how tall your child will be

Your 8-year-old is 128 cm and you need to buy a winter coat in August. How much room should you leave - 3 cm of growth? 7 cm? 12 cm? And will your son end up tall like dad (182 cm) or closer to mum (160 cm)? The school wants a T-shirt size for the end-of-year trip. You have no number to work with.

The solution: two methods, one averaged forecast

The calculator combines the Tanner Mid-Parental Height formula (based on parent heights) with the proportional method (based on the child's current height and the percentage of adult height typically reached at their age). Averaging both methods yields a forecast accurate to about 5 cm.

Adult height forecast - how tall your child will likely be as an adult

Height percentile - where your child ranks among same-age, same-sex peers

Remaining growth - estimated centimeters still to gain before reaching adult height

How to use the Child Growth Predictor - step by step

Child's sex - the Tanner formula adds 13 cm for boys and subtracts 13 cm for girls.
Child's age (years) - determines the percentage of adult height already reached. Range: 1-18.
Child's current height (cm) - measure without shoes, standing straight against a wall.
Father's height (cm) - biological father's height. If unavailable, the estimate loses accuracy.
Mother's height (cm) - biological mother's height.
Read your results - predicted adult height, method comparison table, height percentile and remaining growth.

Tanner formula vs proportional method - decision table

The calculator uses two methods and averages the result. Which one is more accurate? It depends on the child's age.

Parameter	Tanner (MPH)	Proportional method
Formula (boys)	`(father + mother + 13) / 2`	`height / (% of adult height at age)`
Formula (girls)	`(father + mother - 13) / 2`	`height / (% of adult height at age)`
Accuracy	approximately 8.5 cm	approximately 5-7 cm
More reliable at age	1-6 (limited child data)	8-16 (proportions stabilize)
Required inputs	Father + mother height	Child's current height + age
Verdict	Averaging both methods gives the most accurate forecast - approximately 5 cm

Worked examples

Boy, age 8 - current height 132 cm. Father 182 cm, mother 168 cm.
Tanner: (182 + 168 + 13) / 2 = 181.5 cm
Proportional: 132 / 0.72 = 183.3 cm
Combined forecast: 182.4 cm (range 177-188 cm)

Girl, age 6 - current height 118 cm. Father 175 cm, mother 162 cm.
Tanner: (175 + 162 - 13) / 2 = 162.0 cm
Proportional: 118 / 0.65 = 181.5 cm - too high? She is very tall for her age (median: 115 cm). The proportional method overestimates in such cases.
Combined: 171.8 cm - the truth lies closer to Tanner. She is tall now, but genetics suggest ~162 cm.

Boy, age 12 - current height 148 cm. Father 178 cm, mother 165 cm.
Tanner: (178 + 165 + 13) / 2 = 178.0 cm
Proportional: 148 / 0.84 = 176.2 cm
Combined: 177.1 cm - the methods agree well because at 12, proportions are more predictable.

Girl, age 14 - current height 163 cm. Father 185 cm, mother 170 cm.
Tanner: (185 + 170 - 13) / 2 = 171.0 cm
Proportional: 163 / 0.92 = 177.2 cm
Combined: 174.1 cm - she is tall and will likely exceed the Tanner-only estimate.

Boy, age 4 - current height 100 cm. Father 170 cm, mother 158 cm.
Tanner: (170 + 158 + 13) / 2 = 170.5 cm
Proportional: 100 / 0.58 = 172.4 cm
Combined: 171.5 cm (range 167-177 cm). Average height for his genetic background - a consistent forecast.

Percentage of adult height reached by age

How much of their final height has a child already reached? This table is the key to the proportional method.

Age	Boys	Girls	Approx. remaining*
2 yr	49%	52%	~90 cm (B) / ~80 cm (G)
6 yr	65%	70%	~62 cm / ~49 cm
10 yr	78%	84%	~39 cm / ~26 cm
14 yr	92%	98%	~14 cm / ~3 cm
18 yr	100%	100%	0 cm

*Approximate, based on median adult heights: boys ~176 cm, girls ~163 cm.

FAQ - Frequently asked questions

Does height depend only on genetics?

Genetics account for 60-80% of final height. The rest comes from nutrition (protein, calcium, vitamin D), sleep quality (growth hormone is released primarily at night), physical activity and absence of chronic illness. A malnourished child may not reach their genetic potential.

Why do girls stop growing earlier than boys?

Puberty begins about 2 years earlier in girls (around age 10-11 vs 12-13 in boys). Estrogens accelerate the closure of growth plates. Girls typically have their growth spurt earlier but stop growing around age 14-16, while boys continue until 16-18.

What is bone age and can I check it at home?

Bone age is assessed from an X-ray of the left hand and wrist, interpreted by a pediatric endocrinologist. If bone age is younger than calendar age, the child has more time to grow. You cannot assess it at home - it requires clinical imaging and specialist interpretation.

My child is short - when should I see a doctor?

See a pediatric endocrinologist if: height is below the 3rd percentile, growth rate falls below 4 cm per year after age 4, or the child suddenly stops growing. Your pediatrician will review the growth chart and refer for testing if needed.

Is the pubertal growth spurt predictable?

Boys typically grow 8-12 cm per year at peak (around age 13-14), girls 6-10 cm per year (around age 11-12). The spurt begins 1-2 years after the first signs of puberty. Exact timing varies, but the calculator accounts for approximate growth rates by age.

Does the mother's or father's height matter more?

Statistically, both contribute roughly equally - that is why the Tanner formula averages both parents. In practice, a child may take after one parent more than the other. The formula's range of approximately 8.5 cm captures this individual variation.

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