Dog growth plates typically close between 8 and 24 months of age, depending almost entirely on breed size. Small breeds finish growing much earlier than large or giant breeds, and until those plates fully harden into solid bone, a puppy’s skeleton is vulnerable to injury from high-impact activity. Knowing where your dog falls on this timeline helps you make smarter decisions about exercise, nutrition, and spay or neuter timing.
What Growth Plates Are and Why They Matter
Growth plates (also called physes) are soft zones of cartilage near the ends of a puppy’s long bones. They’re the engine of bone growth: new cartilage cells form, harden into bone, and gradually lengthen the leg. Once a dog reaches skeletal maturity, each growth plate mineralizes completely and disappears on X-ray, replaced by solid bone. At that point, the bone can no longer grow longer, and it’s also much harder to damage.
While the plates are still open, they’re the weakest link in the skeletal chain. A force that would strain a ligament or tendon in an adult dog can instead fracture straight through a puppy’s growth plate, potentially disrupting how that bone develops for the rest of the dog’s life.
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 their full skeletal size faster because they simply have less growing to do.
- Toy and small breeds (under 25 lbs): Growth plates generally close between 8 and 12 months.
- Medium breeds (25 to 50 lbs): Closure typically happens around 12 to 15 months.
- Large breeds (50 to 90 lbs): Plates remain open until roughly 15 to 18 months.
- Giant breeds (over 90 lbs): Breeds like Great Danes, Saint Bernards, and Newfoundlands may not reach full skeletal maturity until 18 to 24 months.
These are ranges, not exact dates. Individual dogs within the same breed can vary by a few weeks. The only way to confirm closure is with X-rays, where a veterinarian looks for the point at which the growth plate line is no longer visible between the end of the bone and the shaft.
How Vets Confirm Closure on X-Rays
On a radiograph of a growing puppy, each growth plate shows up as a thin dark line separating two sections of bone. As the dog matures, that line gradually narrows and eventually vanishes. A veterinarian records the plate as “closed” once it’s no longer radiographically visible. Some plates are easier to evaluate than others. Research on Labrador Retrievers found that the growth plate at the top of the shinbone, for instance, becomes difficult to see clearly on certain X-ray views as the dog matures, making it harder to pinpoint its exact closure date compared to plates around the hip or knee.
If you’re planning to start a puppy in agility, dock diving, or another high-impact sport, asking your vet for a set of growth plate X-rays around the expected closure window gives you a concrete answer rather than a guess.
How Spaying or Neutering Affects the Timeline
Sex hormones play a direct role in signaling growth plates to close. When a dog is spayed or neutered before reaching skeletal maturity, that hormonal signal is removed, and the plates stay open longer than they otherwise would. A well-known study compared dogs neutered at 7 weeks, dogs neutered at 7 months, and intact dogs. Growth plate closure was significantly delayed in both neutered groups, but the delay was greater in dogs neutered at 7 weeks.
The rate of bone growth itself wasn’t affected. The bones grew at the same speed; they just grew for a longer period. The practical result was that neutered dogs, especially those neutered very young, ended up with slightly longer leg bones. This is one reason some veterinarians now recommend waiting until after skeletal maturity to spay or neuter large and giant breeds, though the decision involves balancing orthopedic risk against other health factors.
What Happens When a Growth Plate Is Injured
Growth plate fractures in puppies are classified on a scale of increasing severity. The simplest type is a clean break through the cartilage zone itself. More complex fractures extend into the surrounding bone or into the joint surface. The most damaging type is a compression injury that crushes the growth plate, because crushed cartilage cells can’t produce new bone normally.
When a growth plate in one bone of a paired set closes prematurely from injury, the undamaged bone keeps growing while the injured one stops. This creates an angular deformity: the leg curves or twists because the two bones are now different lengths. In the foreleg, this commonly involves the ulna (the thinner bone) closing early while the radius continues to grow, bending the leg outward. Research found these angular deformities most often appear in large breeds during their fastest growth phase, between 3 and 5 months of age, with angular deviations measured anywhere from 7 to 38 degrees.
Corrective surgery can help, especially if caught while the dog still has remaining growth potential. In one study of surgical correction, 43% of treated dogs showed no lameness afterward, while 57% had mild lameness after exercise or rest. Early detection matters enormously, so if your puppy starts limping or you notice one leg looking different from the other, that warrants prompt veterinary attention.
Exercise Guidelines While Plates Are Open
The good news is that puppies don’t need to be kept in a bubble. VCA Animal Hospitals recommends letting puppies run and play freely, allowing them to self-regulate their own activity level. A puppy who flops down when tired is doing exactly what their body needs. Leash walks are a great form of controlled exercise to start early.
What you should hold off on is forced, repetitive, or high-impact exercise that a puppy wouldn’t choose on their own. That means waiting until skeletal maturity before taking your dog on long runs or hikes, having them jump hurdles at full height, or entering them in competitive agility. The distinction is between letting a puppy play (fine) and pushing a puppy through a structured workout (not fine until the plates close).
For giant breeds, the stakes are higher and the wait is longer. Breeds like Rottweilers, Golden Retrievers, Great Danes, and Newfoundlands are especially prone to a group of conditions called developmental orthopedic diseases. The most critical window for these problems is the first 12 months, when the skeleton is most vulnerable to damage from excess weight and mechanical stress. Keeping a large-breed puppy lean is just as important as managing their exercise. Overweight puppies put extra load on immature bones with every step, increasing the risk of skeletal problems during that vulnerable period.
Nutrition During the Growth Period
Large and giant breed puppies benefit from a growth diet specifically formulated for their size. These diets control calcium and calorie levels to promote steady, moderate growth rather than the rapid growth that stresses developing bones. Current recommendations suggest keeping large-breed puppies on an appropriate growth diet until they’re 90 to 99 percent of their adult size, which for many large breeds means staying on puppy food until around 18 months.
After spaying or neutering, the risk of weight gain increases, so adjusting portion sizes or switching to a food formulated for neutered dogs can help keep your puppy at a healthy weight during the remaining growth period. Your vet can track body condition score at each visit to make sure growth is on track without excess weight putting strain on still-open plates.