Child Height Prediction: How Tall Will Your Child Be?

The Mid-Parental Height Formula

The mid-parental height formula is the simplest and most widely used method for predicting a child's adult height. It requires only the biological parents' heights.

For Boys

Predicted height = (Mother's height + Father's height + 5 inches) / 2

In centimeters: (Mother's height + Father's height + 13 cm) / 2

For Girls

Predicted height = (Mother's height + Father's height - 5 inches) / 2

In centimeters: (Mother's height + Father's height - 13 cm) / 2

Worked Example

If the father is 5'10" (70 inches) and the mother is 5'4" (64 inches):

• For a boy: (64 + 70 + 5) / 2 = 139 / 2 = 69.5 inches (5'9.5"), plus or minus 4 inches, giving a range of 5'5.5" to 6'1.5".
• For a girl: (64 + 70 - 5) / 2 = 129 / 2 = 64.5 inches (5'4.5"), plus or minus 4 inches, giving a range of 5'0.5" to 5'8.5".

The Khamis-Roche Method

The Khamis-Roche method, developed in 1994, improves on the mid-parental formula by incorporating the child's current height and weight at a given age. It is designed for children ages 4 and older and does not require a bone age X-ray.

This method uses regression equations derived from longitudinal growth data (the Fels Longitudinal Study) that followed children from birth through adulthood. By factoring in how much a child has already grown relative to their age, it produces tighter predictions: a margin of error of 2.1 inches for boys and 1.7 inches for girls.

The tradeoff is complexity. The Khamis-Roche method uses age-specific regression coefficients that change at every half-year interval, making it impractical to calculate by hand. Our child height predictor automates this calculation.

Bone Age Prediction

The most accurate medical method for predicting adult height is a bone age X-ray, usually of the left hand and wrist. A radiologist compares the X-ray to a standard atlas (the Greulich-Pyle or Tanner-Whitehouse method) to determine how mature the child's growth plates are.

A child whose bone age is younger than their chronological age has more growing time remaining and will likely be taller than a simple mid-parental prediction suggests. Conversely, advanced bone age means the growth plates are closing earlier, and the child may reach a shorter adult height.

Bone age assessments are typically ordered by pediatric endocrinologists when there is a concern about growth disorders, precocious puberty, or delayed puberty. They are not part of routine well-child visits.

When Does Height Growth Stop?

Growth in height depends on the closure of the growth plates (epiphyseal plates) at the ends of the long bones. Once these plates fuse, no further height increase is possible.

• Girls: Typically reach final adult height by age 14 to 16, roughly 2 to 3 years after the onset of their first menstrual period.
• Boys: Typically reach final adult height by age 16 to 18. Boys enter puberty about 2 years later than girls, which gives them more years of pre-pubertal growth and is the main reason why men are, on average, about 5 inches taller than women.

Regression to the Mean: Why Predictions Miss

One of the most common reasons the mid-parental formula over- or under-predicts is regression to the mean. This statistical phenomenon means that very tall parents tend to have children who are tall but not quite as tall as the prediction suggests, and very short parents tend to have children who are short but not quite as short as predicted.

A 2024 study published in Children confirmed that the standard mid-parental formula overestimates the height of children of very tall parents by an average of 2.7 cm and underestimates the height of children of very short parents by a similar amount. The researchers found that adding a regression-to-the-mean correction improved the variance explained from 36% to 40%.

Factors That Influence Adult Height

Genetics (74% of Variation)

Height is one of the most heritable human traits, with twin studies consistently showing heritability around 74 to 90% in well-nourished populations. Hundreds of genetic variants each contribute small amounts to final height.

Nutrition

Adequate calories, protein, calcium, vitamin D, and zinc are essential for reaching genetic height potential. The average American height has increased by about 2 inches over the past century, driven largely by improvements in childhood nutrition.

Health Conditions

Growth hormone deficiency, hypothyroidism, Turner syndrome, celiac disease, and chronic kidney disease can all reduce final height if untreated. Early diagnosis and treatment can often restore normal growth.

Puberty Timing

Children who enter puberty early experience a growth spurt sooner but also stop growing earlier. Late bloomers may be shorter than peers during childhood but often catch up or even surpass early developers in final adult height.

The Bottom Line

Predicting a child's adult height is an imprecise science, but the available methods give useful estimates. The mid-parental height formula offers a quick prediction with about a 4-inch margin of error. The Khamis-Roche method narrows that margin to about 2 inches by incorporating the child's current measurements. And for clinical precision, a bone age X-ray provides the most accurate forecast.

Try our free child height predictorto calculate your child's estimated adult height using both the mid-parental and Khamis-Roche methods.

Frequently Asked Questions