I'm extremely worried about the way I'm growing. For my entire life, I've been in the 70th-80th percentile in regards to height. However, while most of my friends got their growth spurt, I didn't. I've only grown about a half inch in the past year-and-a-half. The trouble is, I just turned 16 last month, and I'm still only 5'8.5". According to the calculator, I'm in stage 3.4, but I'm not so sure that it's correct. I mean, shouldn't I go back up to the 70th percentile? Is this drop a sign that something is wrong?
First, it isn't true that someone in the 70th percentile in childhood will always remain in the 70th percentile into adulthood. In the book, Growth, Maturation, and Physical Activity by Robert M. Malina, Claude Bouchard, Oded Bar-Or, the authors note "... a child's position on growth charts often changes during adolescence because of individual differences in timing and tempo of the growth spurt and sexual maturation. Thus, a child may change position on growth charts. A girl or boy who is advance in maturity and enters puberty early is likely to move upward on the percentiles at this time. On the other hand, a girl or boy who is later maturing is likely to move down on the percentiles until puberty. Growth charts need to be used with care during adolescence."
Second, a growth spurt is generally defined as a marked increase in the rate of growth. In other words, there is a period of time, usually six months to two years when a person grows more rapidly than in childhood. During childhood, growth from about five to puberty is fairly steady, often about 1 to 2 inches per year. During the growth spurt, it can increase by two to four times that rate, or 2 to 8 inches per year. But notice the low end of the scale. Some people grow faster, but not dramatically faster. The result is that they have a growth spurt, but don't really notice it.
In my calculator, I ask questions regarding a large set of characteristics. There are several reasons: some are hard to measure accurately without some experience, some are harder to notice, and some people simply don't have all the characteristics other people have. By looking at development from a number of different angles and blending the result, it is my hope that the calculator is able to give decent estimate as to a person's progress.
Being in stage 3 at sixteen isn't unheard of. It is later than the average, but not excessively so. But I can't say if the calculator is off in your case without knowing more about you or seeing you. If you have concerns, you should ask your doctor the next time you see him. He will be able to give you an accurate assessment of where you are in your growth.