How to use the mid-parental height formula

The formula with examples

This is the mid-parental (target) height formula used in pediatrics. It adjusts for the average 13 cm (about 5 in) height difference between men and women (per the MSD Manual calculator).

	Formula	Dad 178 cm (5 ft 10 in), Mom 165 cm (5 ft 5 in)
Boy	(dad + mom + 13 cm) ÷ 2	178.0 cm (about 5 ft 10 in)
Girl	(dad + mom − 13 cm) ÷ 2	165.0 cm (about 5 ft 5 in)

In inches, use 5 in instead of 13 cm: boys (dad + mom + 5) ÷ 2, girls (dad + mom − 5) ÷ 2.

What ±8.5 cm means

The same source says actual adult height usually falls within about 8.5 cm (3.35 in) either side of the result, roughly two standard deviations. For the boy above, that is about 169.5 to 186.5 cm. A 17 cm span means reading it as “likely in this range,” not “will be 178 cm.”

Siblings get different gene combinations, so their heights can differ a lot.
Children of very tall or very short parents tend to land closer to average (regression to the mean).
The formula says nothing about timing, such as early or late puberty.

What “80% genetic” means

MedlinePlus says about 80% of the variation in height between people is explained by inherited DNA differences, with more than 700 variants identified. The rest comes from environment: nutrition before and after birth, illness, healthcare access and living conditions. The 80% describes differences across a population, not 80% of one child’s height being fixed.

This guide is general information, not medical advice. If your child is much shorter than peers or seems to have stopped growing, talk to your pediatrician, who will use growth charts. A prediction formula alone is never a basis for treatment decisions.

The app’s height histogram

The Android app Genetic Kids Lab uses the same formula (boys +6.5 cm, girls −6.5 cm from the parents’ average) plus random normal variation to generate heights for 1,000 virtual children. The result is a histogram, which is a good way to see the range. Heights in the app are in centimeters.

Parent traits screen with Father 183 cm and Mother 167 cm height sliders — Height input

Set the parents’ heights

Use the Height sliders at the top of Parent traits to set Father and Mother in 1 cm steps.

Children’s height histogram: mean 174.8 cm, range 153 to 199 cm, boys average 181.7 cm, girls average 168.5 cm — Children’s height

Read the children’s height chart

After Simulate 1,000, the Children’s height card shows the overall mean, the range, and the boys’ and girls’ averages. The app’s spread is set wide for teaching, so its range looks broader than the ±8.5 cm guideline.

For learning and fun only. This guide and the app use simplified models to explain genetics concepts. They do not predict or guarantee any real child’s traits and are not a substitute for medical advice or genetic counseling. If you have concerns about health or inherited conditions, talk to a qualified professional.

FAQ

Can a child grow taller than the formula says?

General advice is that enough sleep, balanced meals and activity support healthy growth. For sleep needs by age, see kids’ sleep hours by age. Be skeptical of products that promise extra centimeters.

How is this different from a bone age test?

The formula uses only the parents’ heights. A bone age X-ray is a medical test that looks at the child’s own growth stage.

Genetic Kids Lab - Child Trait Simulator

Pick the parents’ traits and see trait ratios across 1,000 virtual children. An educational, just-for-fun simulator that works offline. Free on Android.

Get it on Google Play