Dog Growth Plate Closure Calculator

What Growth Plate Closure Actually Means

A growth plate, properly an epiphyseal plate or physis, is a band of cartilage sitting between the end of a long bone and its shaft. It is the site where new bone is produced, and it is the reason a puppy’s legs get longer. On a radiograph it shows as a dark line near the joint. Closure is the point where that cartilage has been fully replaced by bone and the line disappears.

Two things follow from that definition and both matter more than the calendar. The first is that an open plate is structurally weaker than the bone and the ligaments around it, so a force that would sprain an adult dog’s joint can instead fracture through the plate in a puppy. The second is that closure is irreversible. Once the plate is bone, the bone cannot lengthen again, which is why a growth deformity is corrected with surgery rather than time.

The timing runs ahead of most people’s expectations. Major growth happens between 3 and 6 months, and dogs reach about 90 percent of adult size by 9 months. That second figure is the source of a lot of premature confidence, because the plates contributing most to bone length are among the last to finish. A dog can look finished and still be months away from skeletal maturity, which is why a single closure age for all dogs was never going to work.

Closure Ages for All 24 Growth Plates

Almost every article on this topic gives a single range, usually 6 to 18 months, and stops. That range is real but it is an aggregate across two dozen separate plates, each with its own schedule. Below is the published breakdown for an average 25 to 30 kg dog. The calculator above scales these windows to your dog’s adult weight.

Source: Von Pfeil DJF, DeCamp CE. The Epiphyseal Plate: Physiology, Anatomy, and Trauma. Compendium: Continuing Education for Veterinarians, July 2009, Table 2.

Twenty four rows raise an obvious question: if they finish months apart, which one actually decides when your dog is done growing?

Why the Last Plate Is the Only One That Matters

Look down the table and the spread is stark. The anconeal process is done at 4 to 5 months. The proximal humerus is still open at 12. If you are deciding whether a dog can start jumping, the average closure age across all plates is useless, because the joint is only as protected as its weakest remaining plate.

This is where the familiar advice to wait until 12 months comes from. It is not an arbitrary round number: in an average sized dog the proximal humerus and the tibial tubercle both run to 12 months, and they are the last to finish. The advice is a restatement of those two rows.

The problem is that the 12 month figure gets repeated for every dog. Scale those same two plates to a toy breed and they finish near 7.8 months, so a small dog owner waits four unnecessary months. Scale them to a giant breed and they run to 17.4 months, so a Great Dane owner who waits 12 months starts hard exercise with more than half the skeleton still open.

All of which assumes the estimate is right for your individual dog. There is one way to stop estimating.

How to Tell If Your Dog’s Growth Plates Are Closed

A radiograph is the only way to know. An open plate appears as a dark radiolucent line running across the bone near the joint, and that line fades and vanishes as the plate closes. There is no external sign that corresponds to it.

Height is the tempting proxy and it is the wrong one. A dog stops gaining noticeable height while plates are still open, because the last months of growth add small amounts to several bones at once. If a decision genuinely turns on closure, such as whether to book a large breed dog’s neuter now or in three months, a single radiograph answers it definitively and is worth asking about.

Knowing the date only matters because of what it changes. The first thing it changes is how far you can walk your dog today.

How Much Exercise Is Safe Before Closure

The working guideline used in canine rehabilitation is the five minute rule: roughly five minutes of continuous forced exercise per month of age, up to twice a day. A four month old puppy gets about 20 minutes per session, a six month old about 30. The calculator applies this to whatever age you enter.

Forced is the load bearing word. It means exercise you set the duration of, such as leash walking, jogging alongside you, or repeated fetch. Free play in a garden is treated separately, because a dog that is allowed to stop will stop. Veterinary sources are consistent that puppies should be allowed to run and play as they want and to self regulate.

Three activities get singled out for restriction before closure: repeated jumping, distance running on leash, and competitive agility. What they share is repetition. A single jump is not the concern; a hundred jumps loading the same open plate is.

It is worth being accurate about the strength of this evidence. The five minute rule is a practitioner heuristic rather than a measured threshold, and rehabilitation specialists note that most activity a young dog chooses for itself does not cause long term joint harm, with traumatic accidents being the larger risk to the plates. Treat the number as a sensible ceiling on forced exercise, not as a line that causes injury the moment it is crossed.

Exercise is the reversible decision. The other one that hangs on closure is not.

Growth Plates, Spaying and Neutering

Sex hormones are the signal that tells growth plates to close. Remove them before the plates have finished and the plates stay open longer, so the long bones keep lengthening and the dog ends up taller than it would otherwise have been. This is not a side effect of the surgery. It is the direct mechanical consequence of removing the closure signal.

The clinical significance comes from what happens when bones lengthen unevenly. UC Davis research covering 35 breeds found raised rates of hip dysplasia, elbow dysplasia and cranial cruciate ligament rupture in several large breeds neutered early, and attributes it to exactly this: the leg gets longer, the joint no longer fits together as well, and the joint carries the mismatch for life. For most large and giant breeds the finding points toward delaying until skeletal maturity.

The finding is breed specific rather than universal. Small breeds, whose plates close near 7 to 9 months anyway, show little of this effect, and there are real counterweights on the other side of the decision including mammary tumour risk and pyometra. The closure date this calculator gives you is one input to that conversation, not the whole of it.

Work the full timing decision through for your breed and sex, or check how much hip dysplasia risk your dog is already carrying before you weigh an early surgery date against it.

What Happens If a Growth Plate Is Injured

Because the plate is the weakest part of a growing bone, trauma that would produce a sprain in an adult dog can fracture through the plate instead. If the damage stops growth on one side, that bone stops lengthening while its neighbour carries on. In the forelimb, where the radius and ulna have to grow in step, the result is an angular limb deformity: the leg bows or twists, and correcting it means surgery.

The practical consequence is about limping. A limp in a growing dog that lasts more than a day or two is worth a vet visit rather than a week of rest, because the window where a growth plate problem is easy to address closes as the deformity establishes itself.

Whether a puppy recovers depends on which kind of setback it was. Growth held back by illness or underfeeding while the plates are still open will usually resume once the cause is fixed, because the cartilage is intact and still producing bone. A plate that has been damaged into closing early will not, since closure is permanent. That distinction is the whole reason the timing of an injury matters more than its severity. Surgical correction and its cost sit outside what this page estimates, and are a conversation for your vet.

Is It Too Late? Reading This After the Fact

Plenty of people find this page after the walks, the stairs and the fetch have already happened, and the honest answer is reassuring. Growth plate injuries are overwhelmingly caused by discrete traumatic events, a fall, a car, a bad landing, rather than by accumulated ordinary exercise. A dog who walked further than the five minute rule suggests and shows no lameness almost certainly did no structural harm.

The signs worth acting on are lameness that persists, reluctance to bear weight, swelling near a joint, or a leg that is visibly turning or bowing compared with the other side. None of those are things to watch and wait on. Their absence, in a dog moving normally, is meaningful evidence that nothing needs fixing.

The questions owners ask most often about all of this are answered below.

Frequently Asked Questions

What to Check Next

Closure timing feeds three other decisions. If you do not yet know the adult weight this calculator needs, predict the adult weight your puppy is heading for and come back. To set the daily activity your dog’s age and build can take once the plates are closed, use the exercise requirements calculator. And because growing too fast is its own orthopedic risk factor, check that your feeding amounts are not pushing growth faster than the skeleton can take.

This page is educational and is not veterinary advice. Closure ages are estimates from published ranges and vary between individual dogs. Last reviewed August 2026.