How does bone age correlate to puberty?

Last updated on April 4, 2023



I’ve recently had a bone age test and it turned out that I am delayed by 3 years. My bone age is 13 years and 8 months while my chronological age is 16 and 8 months. What does this mean? Does it mean I will grow for a longer time? Does bone age correlate with puberty? Will other areas grow alongside my height, such as my penis? Is bone age separate from puberty?


Doctors have long wanted a precise way to measure the progress of a child developing into an adult. Dr. Tanner developed a scale that was based on observations of pubic hair and the genitals for boys or the breasts for girls. He divided his scale into five parts:

  • Stage 1 is for childhood
  • Stage 2 is the beginning of changing
  • Stage 3 is the period of rapid growth in height
  • Stage 4 is the finishing of the changes
  • Stage 5 is adulthood

Tanner’s method is popular, but it is extremely precise because adolescence is only broken down into three phases and it required observations that can be subjective. Other methods have been sought out as a result.

Bone age uses x-ray images of the hand and wrist. The shape of the bones and cartilage in the hand changes as a person changes from child to adult. A master list of various examples (an atlas) was compiled and instead of stages, years were assigned to various points of change. The intention was that the ages were supposed to map to the age of the average boy at that stage of development. Unfortunately, the ages don’t match up to reality and, unfortunately, the scale varies depending on which atlas the technician uses for comparison. Therefore, you should treat the bone age as a numeric scale and not a physical age. The scale technically goes from 0 to 18. In What is the difference between bone age and a Tanner Stage? there is a table that maps a bone age result to Tanner stages.

A bone age of 13 years and 8 months puts you in the latter half of stage 3 or into early stage 4. It means you should be experiencing your rapid growth or it is just recently started to slow down. This is the same period when your penis grows the most in length. It means you are a bit later in developing than the average boy but you are well within the normal range.



Thanks for the reply. If it’s true that I’m in late Tanner stage 3 or early stage 4, how much growth in height could I expect? How much and fast does the penis grow in length and girth during Tanner stage 4? I haven’t been able to find an answer to these questions yet.

Also, I’ve grown 3.5 inches in a year at this point and 2.3 inches in the last 8 months. Both were measurements at the doctor’s office.


Your growth indicates that you are still in Tanner Stage 3. Bone age tests are more precise than Tanner stages, even a bone age test can be off by up to a year on its scale. When your growth rate drops to less than 2 inches per year, you will be in stage 4.

I have no way of determining how much more you will grow. Each person is different because each person inherits a different set of genes. There are several calculators on this site that can give you estimates of your final height at “Predicting Your Adult Height“. I don’t have the information needed to get those estimates. You have to keep in mind that I can’t see you. I only know what you tell me.

In the same way, I can tell you that the male penis grows most in length during stage 3 and that it grows most in girth during stage 4, but I can’t tell you how much your penis will grow. It isn’t a fixed amount for all boys. The range of penis lengths goes from 3 to 8 inches for adult males. The average is 5.25 inches. I have no way of guessing where your penis will fall on that scale. Again, I don’t even know what your current size is, let alone guess what it will end up being.