Most of your skeleton stops growing in length between ages 16 and 22, but the very last bone to fully fuse can take until your mid-to-late 20s. The exact timeline depends on your sex, which bones you’re talking about, and the difference between growing taller and reaching full skeletal maturity.
Growth Plates: Where All the Action Happens
Your bones grow longer from specialized strips of cartilage near each end called growth plates. These cartilage zones are essentially factories: cells on one side multiply rapidly, pushing the bone longer, while cells on the other side harden into actual bone tissue. As long as these plates remain open, your bones can keep lengthening.
The process that eventually shuts them down works like this. Cartilage cells near the center of the growth plate mature, swell, and change the chemical makeup of the material around them, allowing minerals like calcium to move in. Once mineralized, the cartilage can no longer deliver nutrients to the cells inside it, so those cells die off. Blood vessels move into the empty spaces, bringing bone-building cells that replace the old cartilage scaffolding with solid bone. When this replacement catches up to the pace of new cartilage production and overtakes it, the growth plate narrows, then disappears entirely. On an X-ray, a closed growth plate shows up as a thin scar line where the cartilage strip used to be.
The Typical Timeline for Girls and Boys
Girls generally finish growing earlier than boys. At the knee, one of the most studied areas for tracking growth, the earliest signs of complete fusion appear around age 16 to 17 in girls and 17 to 18 in boys. By age 20 to 21, all girls in large studies show fully closed knee growth plates. For boys, that milestone comes at 21 to 22.
But your skeleton isn’t one unified clock. Different bones close on different schedules. The bones in your hands and wrists tend to fuse earlier, which is why doctors often X-ray a child’s hand to estimate how much growth remains. The long bones of the legs and arms close during the late teens and early twenties. The hip bone’s iliac crest, used by orthopedic surgeons to track spinal growth, doesn’t fully ossify until the late teens or early twenties either. Histologic studies confirm that significant vertebral growth persists until that final stage of hip bone fusion is complete.
The collarbone is the slowest finisher. The inner end of the clavicle is the last growth plate in the entire skeleton to close. Partial fusion there can show up anywhere from age 15 to 36, and while some people see complete fusion as early as 18 or 19, others still show signs of incomplete closure into their mid-20s. Researchers consider 30 the upper limit for full skeletal maturity when using the clavicle as a marker.
Estrogen Is the Real Off Switch
You might assume testosterone shuts down growth in boys and estrogen does the job in girls. The reality is simpler: estrogen closes growth plates in everyone. In boys, testosterone gets converted into estrogen by an enzyme called aromatase, and it’s that converted estrogen that signals the growth plates to fuse. Studies of men who lack either the ability to produce estrogen or the ability to respond to it show that their growth plates never close, and they continue gaining height well into adulthood. Giving these men high doses of testosterone alone does nothing to advance bone age or trigger fusion.
This is why girls stop growing earlier. They reach higher estrogen levels sooner during puberty, and their growth plates receive the shutdown signal at a younger age. Boys go through a longer growth phase partly because their estrogen levels rise more gradually, giving the growth plates more time to keep working before the critical threshold is reached.
Why Some People Stop Growing Earlier or Later
Nutrition plays a measurable role in how quickly your skeleton matures. In studies of children from low-income settings, those who consumed more total calories had more advanced skeletal maturity, were less likely to be stunted, and grew faster. The effect was driven by overall calorie intake rather than any single nutrient like protein or calcium, though severe calcium deficiency (under 300 milligrams per day) can cause rickets on its own regardless of other factors.
Children who are chronically malnourished show significant delays in skeletal maturation. Their bones are essentially running behind schedule, with growth plates staying open longer than expected for their age. This doesn’t mean they end up taller. A delayed growth plate combined with poor nutrition typically results in shorter stature, not extra growth. The skeleton is waiting for resources that never arrive in sufficient quantity.
Certain hormonal conditions can also shift the timeline. In people with very delayed or absent puberty, growth plates may remain open well past the typical age of closure because estrogen levels never rise enough to trigger fusion. Girls with isolated hypogonadotropic hypogonadism, for example, can have unfused growth plates at age 20. On the other end, children who enter puberty unusually early may stop growing sooner, since their estrogen exposure begins ahead of schedule.
Height Stops, but Your Skeleton Doesn’t
Once growth plates fuse, you will not get taller. No supplement, exercise, or stretching routine can reopen a closed growth plate. That said, your bones are far from finished changing.
Peak bone mass, the point at which your skeleton reaches its maximum density and mineral content, comes several years after you stop getting taller. For women, peak bone mineral content arrives around age 22, and peak bone density around age 22 to 23. Men reach peak bone mineral content around age 24 and peak density closer to age 27. This means your bones are still getting denser and stronger for years after your last inch of height.
Even after peak bone mass, your skeleton never truly stops working on itself. Bone remodeling is a lifelong process where specialized cells break down old or damaged bone and replace it with fresh material. Cells embedded throughout your bone tissue act as stress sensors, detecting mechanical forces from movement, exercise, and gravity, then sending chemical signals that direct where bone should be reinforced or removed. This is why weight-bearing exercise strengthens bones at any age, and why prolonged inactivity weakens them. Your skeleton is constantly adapting its architecture to match the demands you place on it.
How Doctors Check if You’re Still Growing
The standard method is a bone age X-ray, typically of the left hand and wrist. Doctors compare the appearance of your growth plates and the shapes of the small bones to a reference atlas of images from known ages. Open growth plates appear as clear gaps between the end of the bone and the shaft. As fusion progresses, those gaps narrow and eventually vanish, leaving behind a faint scar line.
For spine-specific growth, orthopedic surgeons use the Risser scale, which tracks the hardening and fusion of a strip of cartilage along the top of the hip bone. The scale runs from 0 (no ossification visible) to 5 (complete fusion). Only stage 5 reliably indicates that vertebral growth has stopped. This distinction matters especially for adolescents being monitored for scoliosis, where knowing whether the spine is still growing determines the course of treatment.
Your bone age and your actual age don’t always match. A 14-year-old with delayed skeletal maturity might have bone age readings closer to 12, meaning more growth remains. A 14-year-old in early puberty with advanced bone age might be closer to finished. The X-ray tells a more accurate story than the calendar.