# How tall will I be? How adult height is estimated for teenagers, and why it is always a range > A teenager's adult height is estimated as a range, not a single number. What the Khamis-Roche method uses, how accurate it is, why the range widens, and what no calculation can promise. Published: 2026-09-28 · Page: https://finalstat.app/en/blog/how-tall-will-i-be ## The short answer Nobody can know for certain how tall you will be as an adult. What can be calculated is an **estimate with a range**. The most widely used method that needs no X-ray, the **Khamis-Roche** method (*Pediatrics*, 1994), combines your age, your sex, your height and weight today, and your mother's and father's heights. In the original study, averaged across all ages, **90% of estimates were within 5.3 cm (2.1 in) of the real adult height for boys, and within 4.3 cm (1.7 in) for girls**. That is why an honest result always comes with its range: 9 in 10 estimates fall within it. No habit, exercise or supplement moves that calculation upward. Sleeping, eating and moving well **protect** the growth your body already has under way. ## What the estimate uses The Khamis-Roche method uses four values, plus your sex at birth: - **Your exact age**, in years and months. - **Your height today**, measured without shoes. - **Your weight today.** It refines the estimate. - **Your parents' average height**: your mother's and your father's, added together and divided by two. It does not use an X-ray. Some methods measure bone age from an X-ray of the hand; this one does not need it, which is what makes it possible with a tape measure and a wall. ## How the Khamis-Roche method works Khamis and Roche followed children in the Fels Longitudinal Study, in the United States, until they finished growing. From that data they published, for each sex and for each half-year of age between **4 and 17.5 years**, four fixed numbers: one for height, one for weight, one for the parents' average height, and a constant. The estimate is the sum of each value multiplied by its number. Three details change the result and are worth knowing: 1. **Age is not rounded.** If you are 14 years and 3 months old, the numbers are interpolated between the rows for 14 and for 14.5. 2. **The parents' average is a plain average.** Another widely quoted formula adds or subtracts 13 cm depending on sex; that is a different method, and mixing the two gives a wrong result that looks reasonable. 3. **There is no estimate outside ages 4 to 17.5.** The study's table ends there. From 18 on, growth is usually close to complete. ## Why it is always a range The study published its own margin of error. Averaged across ages, half of the estimates were within **2.2 cm** for boys and **1.7 cm** for girls, and 90% within **5.3 cm and 4.3 cm**. A single number, such as "you will reach 176", hides that margin and sounds more certain than it is. So an honest result is written like this: **176 cm · 171-181**. The number is the central estimate, and the span is where 90% of cases fall. The range is not fixed: - **It widens when a value is missing.** If you do not know your weight or one parent's height, a typical value stands in for it and the range grows to cover every value it could have had. - **It never shrinks through rounding.** The low end is rounded down and the high end up. ## What your percentile is, and what it is not Your percentile compares your height **today** with other people of your age and sex, using the 2000 growth charts of the United States CDC. The 60th percentile means that out of every 100 people of your age and sex, about 60 are shorter than you. It is not a grade and it is not a forecast. The 20th percentile is not worse than the 80th, and today's percentile does not say which percentile you will end up in as an adult. What is sometimes worth a look is a large change between one measurement and the next. ## What no calculation can promise - **It does not know your health.** It knows nothing about your medical history, your diet, the timing of your puberty or your genetics beyond your parents' heights. Two people with the same values can end up at different heights. - **It does not detect problems.** If something about your growth needs checking, a pediatrician finds it, with a real check-up. - **It comes from one population.** The coefficients come from a study in the United States. In other populations the real margin may differ. - **Habits protect growth; they do not increase it.** Sleeping too little, eating poorly or being ill for a long time can keep someone from reaching the height they would have reached. Sleeping well takes no one beyond that, and no pill, supplement or stretch lengthens bones. ## When to talk to a pediatrician Talk to a pediatrician if your percentile drops a lot between two measurements, or if anything about your growth worries you. An estimate does not replace a check-up, and no result should delay one. ## How FinalStat applies it FinalStat is an app for teenagers that uses this method. It calculates your estimate on your phone, with the Khamis-Roche coefficients and the CDC charts inside the app, and always shows it with its range and your percentile. If you do not know one parent's height, it uses your country's average adult height published by NCD-RisC, or a global average where it has none, and widens the range. Seeing your result is free. [The medical disclaimer](/en/medical-disclaimer) explains what the app is and is not. ## Key facts - Adult height is estimated as a range, not as an exact number. - The Khamis-Roche method (1994) uses age, sex, height, weight and the parents' average height, with no X-ray. - It estimates between ages 4 and 17.5. - In the original study, averaged across all ages, 90% of estimates were within 5.3 cm (2.1 in) of the real height for boys and within 4.3 cm (1.7 in) for girls. - When a value is missing, the range widens to cover what that value could have been. - A percentile describes your height today against your age and sex; it does not predict your adult percentile. - Habits protect growth; none of them increases it. - An estimate is not a diagnosis. For any concern, see a pediatrician. ## Sources - Khamis HJ, Roche AF. Predicting adult stature without using skeletal age: the Khamis-Roche method. *Pediatrics*. 1994;94(4):504-507. [doi:10.1542/peds.94.4.504](https://doi.org/10.1542/peds.94.4.504). Erratum: *Pediatrics*. 1995;95(3):457. - Kuczmarski RJ, Ogden CL, Guo SS, et al. 2000 CDC growth charts for the United States: methods and development. *Vital Health Stat* 11(246). National Center for Health Statistics, 2002. [CDC data files](https://www.cdc.gov/growthcharts/zscore.htm). - NCD Risk Factor Collaboration (NCD-RisC). A century of trends in adult human height. *eLife*. 2016;5:e13410. [doi:10.7554/eLife.13410](https://doi.org/10.7554/eLife.13410). - NCD Risk Factor Collaboration (NCD-RisC). Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories. *The Lancet*. 2020;396(10261):1511-1524. [doi:10.1016/S0140-6736(20)31859-6](https://doi.org/10.1016/S0140-6736(20)31859-6).