How Tall Will My Child Be? Predicting a Child's Adult Height

By: Adriana Maria Tavares Gomes, MD & Lynne M. Bird, MD, FAAP

Parents often wonder how tall their toddler or preschooler might be when they grow up. Grade schoolers and young teens may ask, "How tall will I be?" It is a natural question for parents and children. Plus, besides being a little fun to try and predict how tall a child might be, pediatricians also find it helpful to make sure a child is growing as expected.

While no one has a crystal ball, there are ways parents and pediatricians can make an educated guess about their child's height potential.

How to predict your child’s adult height

The most accurate method of height prediction comes from a child’s current height together with a bone age assessment, which is determined by an X-ray of the hand and wrist. But there are several methods you can use at home to get an idea of how tall your child may eventually become.

The mid-parental method/Tanner’s formula

The most common way to estimate a child's adult height is to base it on the parents' heights, since height is largely influenced by genetics. In fact, studies suggest that about 60% to 70% of differences in height are determined by their parents’ height.

A slightly more complex method of predicting your child's height is known as the "mid-parental method." To use this methold, add together the measured heights of the biological mother and father in inches and divide by 2, and then make an adjustment based on the sex of the child.

• For a boy: [(mother's height + 5 inches) + father's height] divided by 2
  
  
• For a girl: subtract 2½ inches [(father's height – 5 inches) + mother's height] divided by 2

Note: This is just a very rough estimate of the average height of how tall a child will be when fully grown. You can expect a margin of error of about 4 inches up or down. The taller the parents, the taller the child is likely to be; similarly, the shorter the parents, the shorter the child.

The 2 x 2 method (doubling a child's height at 2 years old)

Did you know that the earliest growth spurt, from baby to toddler, actually accounts for roughly half of a child's adult height? This helps shed light on another simple method to predict adult height, which is to double the child's height at age 24 months/2 years old.

Girls develop more quickly, so doubling their height at 18 months old can also be used as an estimate of how tall they will be as adults.

Just keep in mind that this is a popular rule of thumb rather than a medically validated prediction tool. And while this method has been around for a long time, no research exists to show its accuracy.

What growth charts can tell you

Regular measurements of a child's height, weight and head size plotted on a growth chart are a good way to see if your child is growing as expected. At each well-child visit, pediatricians compare your child's measurements with standardized growth charts and past measurements to assess growth velocity, or how quickly they are growing.

Children who consistently follow their growth curve are more likely to reach a height within their expected genetic range. When growth patterns are unusual, pediatricians may take additional body measurements, such as arm span or the ratio of the upper and lower body segments. These measurements can provide clues to health conditions that may affect adult height.

In older children, growth charts can also provide clues about the onset of puberty, which plays an important role in adult height. Children who enter puberty earlier often experience a growth spurt sooner but may stop growing at a younger age. Those who enter puberty later may continue growing for a longer period.

Because the timing of puberty varies widely, some children naturally develop earlier or later than their peers. However, breast development before age 8 in girls or other signs of unusually early puberty should be evaluated by a doctor.

Family history & genetics

Height and growth patterns usually run in families. Height is also a "polygenic" trait, meaning that it can be influenced by the combined effects of many genes, as opposed to being controlled only by a single gene.

That's why your pediatrician will often ask about the height of biological parents and other close relatives. They may also ask about growth patterns, like how fast and at what age you grew during your. Were you short in grade school but kept growing after all of your friends stopped? Did you go through puberty early or late? These may be important clues for your child's pediatrician.

What else affects a child's height?

While genes play a huge part in height, (shorter parents usually have shorter children, for example), other factors have an impact on how tall your child grows. These include:

Nutrition

Good nutrition is essential for healthy growth. Inadequate calories, protein or key nutrients can slow growth and affect height. Poor nutrition, inadequate protein and micronutrient (vitamins and minerals) deficiency can affect height.

A child with overweight or obesity is often taller than classmates, although that does not necessarily mean that they will be taller as an adult. Excess body weight can sometimes cause bones to mature faster, which may lead to growth stopping sooner. On the other hand, children who are very underweight may grow more slowly and be shorter than expected for their age.

Hormones