Puppy growth plates typically close between 6 and 18 months of age, depending almost entirely on breed size. Small breeds finish as early as 6 to 8 months, while giant breeds like Great Danes and Mastiffs may not fully close until 18 to 24 months. Until those plates solidify into bone, they’re the most vulnerable part of your puppy’s skeleton.
What Growth Plates Actually Do
Growth plates are thin layers of cartilage near the ends of your puppy’s long bones, including the legs, shoulders, and hips. They act as the engine of bone growth. Cells in the cartilage multiply, stack into columns, and then gradually harden as tiny mineral spheres form in the spaces between them. These spheres grow and merge into solid mineral deposits, which are then slowly remodeled into true bone. This process repeats continuously, pushing the bone longer from both ends, until hormonal signals tell the plate to shut down for good.
Once the cartilage fully mineralizes and converts to bone, the growth plate disappears on X-rays and the bone stops lengthening. At that point, the area is as strong as the surrounding bone. Before that happens, though, the soft cartilage is structurally weaker than the bone or ligaments around it, which is why injuries tend to happen there rather than in the middle of the bone itself.
Closure Timeline by Breed Size
The single biggest factor in when growth plates close is how large your dog will be as an adult. Smaller dogs reach skeletal maturity faster because they simply have less growing to do.
- Toy and small breeds (under 25 pounds adult weight): Growth plates generally close by 6 to 8 months of age.
- Medium breeds (25 to 50 pounds): Closure typically happens around 12 months.
- Large breeds (50 to 80 pounds): Most plates close between 12 and 16 months.
- Giant breeds (over 80 pounds): Growth plates may remain open until 18 months, and some breeds like Mastiffs may not reach full skeletal maturity until 24 months.
These are averages. Individual puppies vary, and not every growth plate in the body closes at the same time.
Not All Plates Close at Once
Growth plates don’t shut down simultaneously across the skeleton. They close in a staggered sequence, generally starting closer to the body’s core and finishing at the extremities. In the front legs, the upper arm bone tends to fuse at the shoulder end later than the elbow end. The lower forearm bones (radius and ulna) close at the wrist end last. In the hind legs, the hip socket has some of the latest-closing plates in the entire body. Certain parts of the pelvis don’t fully fuse until well past a year, and one pelvic joint can remain partially open for several years.
This staggered closure is why your puppy’s legs might look a bit awkward during adolescence. Different bones are finishing growth on different schedules, which can make proportions look temporarily off.
How Spaying and Neutering Affects Timing
Sex hormones, particularly estrogen and testosterone, play a direct role in signaling growth plates to close. Both hormones accelerate the calcium deposition that converts cartilage to bone. When a puppy is neutered or spayed before reaching skeletal maturity, the removal of those hormones can delay growth plate closure.
Research in cats has confirmed that neutered males show significantly delayed closure in several key growth plates compared to intact males, including the knee and hip areas. The same mechanism applies to dogs. The practical result is that early-neutered animals often end up with slightly longer limbs than they would have had otherwise, because the bones keep growing for a longer period. Some veterinary guidelines suggest that early neutering in large breeds can push growth plate closure out to as late as 22 months. This is one reason many veterinarians now recommend waiting until after skeletal maturity to spay or neuter large and giant breed dogs.
Why Open Growth Plates Are Vulnerable
Because growth plate cartilage is softer than surrounding bone, it’s the weak link in a puppy’s skeleton. A force that would cause a sprain or bruise in an adult dog can fracture through the growth plate in a puppy. The consequences depend on severity. A mild injury may heal without lasting effects, but if part of the growth plate is damaged badly enough to stop functioning, the bone can develop permanent problems.
When only a portion of the plate is destroyed, the undamaged section keeps growing while the injured section doesn’t. This creates a twisting or bending of the limb as the bone grows unevenly. In the forearm, where two bones (the radius and ulna) sit side by side, an injured plate on one bone can cause the other to push the wrist into a visible angular deformity. If the final bone ends up less than 20 to 25 percent shorter than normal, most dogs compensate well because they naturally walk with slightly bent legs. But more severe shortening or twisting often requires surgical correction.
Signs of a growth plate injury include sudden limping, swelling near a joint, reluctance to bear weight, or a limb that starts to look crooked over the following weeks. These injuries need veterinary attention quickly, because the window to intervene before permanent deformity sets in is relatively short.
Safe Exercise While Plates Are Open
The goal isn’t to restrict your puppy to a crate until their plates close. Puppies need movement for healthy bone development, coordination, and mental stimulation. The key is choosing the right types and amounts of activity.
For puppies between two and four months old, exercise sessions of 15 to 30 minutes work well. By four to six months, you can extend that to 45 to 60 minutes. The best exercise at this age is off-leash exploration in a safe, enclosed area with soft and varied terrain. This lets your puppy move at their own pace, change direction naturally, and develop balance and spatial awareness. Walking on a short leash at a brisk human pace is actually less ideal for young puppies because it forces repetitive, concussive movement patterns without the variety of free play.
Activities to avoid until growth plates have closed:
- Jogging or cycling alongside your puppy, which forces sustained high-impact movement
- Repetitive ball-chasing, especially with launchers that send balls long distances and encourage sudden stops and hard landings
- Agility jumps and obstacles that involve repeated high-impact landings
- Long runs on hard surfaces like pavement or concrete
Endurance training, structured running, and high-impact sports should wait until after skeletal maturity: around seven months for small breeds, and 10 to 14 months for large breeds. If your dog was neutered early, consider pushing that timeline out further to account for potentially delayed closure.
How Vets Confirm Plates Have Closed
The only reliable way to know whether your puppy’s growth plates have closed is through X-rays. On a radiograph, an open growth plate appears as a dark line near the end of the bone, because cartilage doesn’t show up the way mineralized bone does. Once the plate has fully ossified, that dark line disappears and the bone looks continuous from end to end. Your vet may recommend X-rays before clearing your dog for high-impact activities, particularly for large or giant breeds where the timeline is less predictable, or for dogs that were neutered early.