Predicting Maximum Height

One of the most intuitive features of the Tall or nah height calculator is its ability to predict the maximum height of someone whose height is still increasing. This prediction is included in every height calculation that Tall or nah makes if the subject is older than 2 and younger than 21 years old. This prediction is, of course, a statistical guess, but on average it's a relatively accurate one. This article will explain why that is, how the prediction is made, and what factors can impact the actual height the subject will reach.

Calculating the percentile

To understand how a height calculator like Tall or nah can make a max-height prediction, it is important to first understand how it computes the subject's height percentile, since the percentile is the key metric used to make the prediction. When a person enters their information (current height, age, and biological sex) into the calculator, the calculator must first determine who that person's peers are. If the subject is a biological male, then the calculator will use the male height distribution curve. If the subject is a biological female, then the calculator will use the female height distribution curve. After the appropriate curve has been selected, the calculator must then isolate the section of the curve that matches the subject's age. Because height can increase relatively rapidly month over month, age must be computed in total months, not years. The subject must be compared against their closest-matching peers, which must not only be in the same biological sex, but within 1 month of the subject's age.

Once the calculator has identified the subject's peers on the curve, the subject's input data is then compared against them. This comparison will yield what the calculator labels a "percentage score", which is more technically a percentile. This number is the percentage of those peers that the subject is taller than. For example, if the percentage score is 64%, then the subject is in the 64th percentile, and is taller than 64% of his/her same-sex and same-age peers. If the percentile is 1%, then the subject is in the first percentile, and is taller than only 1% of his/her same-sex and same-age peers. The percentile can never technically reach 0 or 100, but it can come so close that the calculator may deem it virtually 0 or virtually 100.

Reverse calculating the percentile

Once the calculator has obtained the subject's percentile, the calculator will go back to the same height distribution curve as before and reverse calculate the height that corresponds to that percentile in the oldest peer group. To do this, the calculator must compute the number of standard deviations from the median of the subject's percentile, and use it to make a new calculation using the lambda, mu, and sigma values that describe the peer group at the end of the curve, where the age is at its maximum value. Therefore, what the prediction really does is determine the height of the oldest people in the subject's current percentile on the subject's height distribution curve.

The reason that this method can be employed to make a max-height prediction is because population data has shown that height percentiles tend to track consistently over time. That is, children who are tall for their age are likely to remain tall into adulthood, and children who are short for their age are likely to remain short into adulthood. It is not typically the case that a person's height percentile is volatile as their height increases. In fact, any volatility is inversely correlated to age, and will consistently decrease over time. This is because height percentile is less likely to change at the end of the curve versus the start of it. Therefore, subjects who are old enough to calculate their own max-height predictions, such as adolescents, will yield results with greater accuracy than subjects who are too young to use the calculator, such as infants.

How tall the subject will actually end up being is really anyone's guess, however. But of all the guesses that can be made, the one made by Tall or nah may be the most data-driven. Still, several real-world factors—such as genetics, nutrition, health, and hormonal development—can influence the actual height a person reaches. Let’s take a closer look at these factors and how they can shift the final outcome.

Biological factors that influence height

The most influential factor that determines a person’s maximum height is genetics. Everyone inherits a unique set of genes from their parents that establish a general range of potential height. This is why taller parents tend to have taller children and shorter parents tend to have shorter children. However, genes do not operate in isolation. Height is a polygenic trait, meaning that it's influenced by a number of genes—possibly hundreds—that each contribute a small effect. Therefore, there is no single "height gene" that determines maximum height. Instead, the combined effect of many genes creates a height range within which environmental factors—like nutrition and health—can push a person closer to the upper or lower end of their potential.

If genetics is seen as the blueprint for height, nutrition is seen as the driver that determines how fully that blueprint is realized. Proper nutrition is especially critical during infancy when growth is most rapid. A diet that provides sufficient water, protein, fat, and carbohydrates, while providing the necessary spectrum of vitamins, minerals, and trace elements, is essential for growth throughout the body, including height. Deficiencies in any of these nutrients can slow growth and, in severe cases, cause stunting, even in individuals who are genetically predisposed to be tall. Without adequate nutrition, the genetic potential for height remains unrealized, underscoring the critical role diet plays in transforming biological possibility into physical reality.

Beyond genetics and nutrition, overall health and hormonal development also play a decisive role in determining height. Chronic illnesses or frequent infections can divert the body’s resources away from growth, while adequate sleep and a healthy endocrine system ensure that growth hormones—especially human growth hormone (HGH) and thyroid hormones—are released in the right amounts at the right times. Puberty is another critical stage, as the timing and balance of sex hormones influence the final growth spurt and the eventual closure of growth plates in the bones. Together, these factors form the biological foundation that ultimately dictates how tall a person will become.