When do puppies stop growing?

Why bigger dogs grow longer

More bone, more time. The growth plates — the soft strips of cartilage at the ends of the long bones — are where new bone gets built during puppyhood. Once the plate hardens into bone, the bone stops growing. Smaller frames have less bone to lay down, so the plates close fast. Bigger frames take longer.

That is why a Yorkie is fully grown at 7 months and a Mastiff is still building at 22 months. Same biology, different timeline. The cost of being big is a long, slow build — and during that build, the joints are vulnerable. This matters more than most owners realize, especially for the big-breed puppies.

Toy and small breeds: 6 to 8 months

Yorkies, Pomeranians, Chihuahuas, French Bulldogs, Pugs, Dachshunds, mini Poodles. Adult weight from a few pounds up to about 25. These dogs hit adult size first — most are done by 7 months, almost all by 8.

What that means in practice: switch to adult food around 9-12 months. Adult-size harness and collar usually fit by 6 months. Spay/neuter timing for small breeds is typically discussed around 6 months because the bones are basically there.

One real catch with small breeds: pet versions are usually heavier than the breed standard says. A "teacup" Yorkie sold as 4 pounds often grows to 8-10 pounds. Pet Pomeranians land at 8-12 pounds even though show standard caps at 7. Body shape, not breed standard, is the better gauge once a dog has stopped growing.

Medium breeds: about 12 months

Beagles, Cocker Spaniels, Border Collies, Australian Shepherds, Pembroke Welsh Corgis, Boxers (mid-end), Standard Schnauzers. Adult weight 25 to 55 pounds. The classic 1-year-birthday rule actually fits this group reasonably well — most are at adult weight by 12 months and at adult height a month or two before that.

Adult food switch around 12-14 months. Adult harness usually fits by 9-10 months. Body still fills out for a few months after weight peaks — a 12-month-old Lab-sized dog is at adult weight but still has a slight lankiness that goes away around 18-20 months.

Large breeds: 14 to 16 months

Labrador Retrievers, Golden Retrievers, German Shepherds, Doberman Pinschers, Rottweilers (small end), Standard Poodles, Siberian Huskies. Adult weight 55 to 90 pounds. These dogs blow past the 1-year mark still growing — usually adding a few pounds and a touch of height between 12 and 16 months.

This is also the size class where slow-growth feeding starts to matter. Pushing a large-breed puppy to adult size by 12 months instead of 16 is a real risk to the joints — too much calcium, too many calories, and the bones grow faster than the joints can handle. Vets routinely flag "your puppy is big for the age" in this group as a feeding question, not a brag.

Use a food labeled for "growth of large-size dogs (70 lb or more as an adult)" until 14-18 months, even if weight has plateaued at 12. The growth plates are still active. Skip the calcium supplements your aunt mentioned at the family dinner — for big breeds, more calcium is worse, not better.

Giant breeds: 18 to 24 months

Great Danes, Mastiffs (English, Bullmastiff, Tibetan), Bernese Mountain Dogs, Saint Bernards, Newfoundlands, Great Pyrenees, Irish Wolfhounds. Adult weight over 90 pounds, often well over. These dogs grow longest. A Great Dane at 12 months is at roughly 87 percent of adult weight. A Mastiff at 12 months is at 75-80 percent. Both still have months of growing ahead.

Mastiffs in particular are the slowest. AKC notes Mastiffs "may not even reach their fully grown size until 24 months of age." If your Mastiff is still gaining weight at 22 months, that is normal. Most other giant breeds are at adult size by 18-20 months.

Giant-breed feeding is the strictest. Stay on large-breed-puppy food until at least 18 months. Keep workouts low-impact for the first 12-14 months — fetch on grass is fine, mile-long jogging on pavement at 4 months is not. Growth-plate injuries in giant breeds are the kind of thing that show up as a chronic limp 5 years later, not as an immediate problem. The careful first 18 months pay off across the whole lifespan.

Height stops before weight stops

One thing that confuses owners: dogs reach adult height before they reach adult weight. Most dogs hit their final height within a few weeks of the size-class cutoff above. After that, they keep filling out — adding muscle and a bit of body mass — for another 6 to 12 months.

So a 12-month-old Lab is at adult height but still looks lean and lanky. By 18-20 months, the same dog has filled out the chest and shoulders and looks like the adult version of itself. That filling-out is normal and healthy — it's not weight gain in the body-condition-score sense. A 1-year-old at body shape 5 is still a body shape 5 at 2.

Questions worth asking

Sources

Full source list with verbatim quotes lives at /methodology. Specific to this guide:

• American Kennel Club. "When Does My Puppy Finish Growing?" — size-class timing for small (6-8 months), medium (~12 months), large (12-18 months), giant (12-18 months, Mastiffs to 24). akc.org puppy finish growing
• American Animal Hospital Association. 2019 AAHA Canine Life Stage Guidelines. Puppy life-stage definitions and the puppy-to-adult food-transition timing recommendations. aaha.org canine-life-stage-guidelines
• WALTHAM Petcare Science Institute. Puppy growth charts and growth-curve research — the canonical reference for size-class growth percentages. waltham.com/resources/puppy-growth-charts
• National Research Council. Nutrient Requirements of Dogs and Cats, 2006. Calcium and phosphorus requirements during the growth-plate-active window — the basis for the slow-growth feeding guidance for large/giant breeds. nap.nationalacademies.org/catalog/10668

Pairs with this guide: the puppy growth calculator (predicts adult weight from current weight + age + size band), the dog age calculator (for after the puppy years), and the dog body condition score guide (the body-shape gauge that takes over once growth is done).