When Do Dogs Stop Growing?

Most dogs reach adult size between 10 and 24 months, and the timing depends almost entirely on how big the dog is going to be. Small and medium dogs are usually done growing by 10 to 12 months. Large and giant breeds keep growing for a year or more after that, sometimes not finishing until 18 to 24 months old.

That range is wide because size class changes the whole growth curve. It changes how fast a puppy grows, how long the growth period lasts, and when the growth plates that drive bone length finally close.

The short answer, by size

The MSD Veterinary Manual states that growth rate "plateaus after 6 months" across the board, with skeletal maturity "completed by 8-12 months in small and medium breeds" and "10-16 months" in large and giant breeds. VCA Animal Hospitals and the Purina Institute describe the same split: small and medium by 10 to 12 months, large and giant by 18 to 24 months.

A third source, dog-care-knowledge.com, cites the Hawthorne et al. 2004 study in the Journal of Nutrition for a similar milestone: "Toys, small-, and medium-sized dogs achieve adult body size by 9 to 10 months of age. Giant breeds do not achieve 99% of their adult body size until 11 to 15 months of age." That lines up closely with the MSD and VCA figures. Exact months differ slightly across sources, which is normal since "adult size" gets measured a little differently from study to study, but the pattern holds regardless of which one you read: small dogs stop growing first, and every step up in adult size adds months to the timeline.

Why big dogs take so much longer to grow up

The best-documented data point on this comes from a puppy-weight calculator site that draws on the Hawthorne 2004 research: a toy breed puppy reaches about 50% of its adult weight at roughly 12 weeks old, while a giant breed doesn't hit that same 50% mark until roughly 26 weeks old (calculatorsfordogs.com). A toy breed is already halfway grown by 3 months; a giant breed needs twice that long, 6 months, to reach the same point.

That gap reflects a real biological difference. Giant breeds are built to add far more total mass than toy breeds, so growth spreads over a much longer runway. Packing that much growth into the same short window as a toy breed would stress developing bones and joints, so larger breeds grow more slowly and for longer instead.

This is also the logic behind the Salt et al. 2017 PLOS ONE study, the largest study of its kind on puppy growth. Researchers analyzed bodyweight records from more than 6 million young dogs, including 5.5 million individual dogs between about 10 weeks and 2.25 years old, at primary care veterinary hospitals in the United States. They grouped dogs into five adult-weight categories, from under 6.5 kg (about 14 lb) up to 30-40 kg (66-88 lb), and modeled a separate growth curve for each, because a single "average puppy" curve does not describe any real dog well.

That same research, run with University College London, became the basis for the WALTHAM Petcare Science Institute's puppy growth charts, built from over 6 million measurements from 50,000 puppies, using methods similar to the WHO's child growth standards. The charts use the same five weight bands and are valid up to 40 kg (88 lb) of predicted adult weight; above that, a vet needs an individualized chart.

Growth plates: the mechanism behind the timeline

The size-based timeline above tracks something happening at the skeletal level. The MSD Veterinary Manual's term "skeletal maturity" refers to the point where a dog's growth plates, areas of developing cartilage near the ends of long bones, finish converting to solid bone and close. Once a growth plate closes, that bone stops getting longer. That process wraps up around 8 to 12 months in small and medium breeds, and 10 to 16 months in large and giant breeds, matching the adult-size timelines above.

How to estimate your dog's adult size from its current weight

If your puppy is still growing, two formulas give a rough read on adult size, and it helps to know their limits.

The simplest method, often attributed to Wisdom Panel veterinarians, is to take your puppy's weight at 4 months and double it. A 15-pound puppy at 4 months would project to roughly 30 pounds as an adult. Wisdom Panel flags this as its least accurate method, since a flat doubling ignores breed-size differences: toy breeds are already well past the halfway point of adult weight by 4 months, so doubling tends to overestimate them, while giant breeds are still well short of halfway at that age, so doubling tends to underestimate them.

A second method, published by Omni Calculator, extrapolates in a straight line: divide current weight by current age in weeks, then multiply by 52. Omni Calculator is upfront that this assumes dogs mature in about 12 months on average, "with variations ranging from 8 months for smaller breeds to 16 months for larger ones," and does not account for those variations. Because real puppy growth is not a straight line, this formula is least accurate for large and giant breeds, whose growth continues well past week 52 and slows rather than climbing steadily the whole way.

Both formulas are useful for a ballpark, and neither replaces knowing your puppy's likely adult size class. The puppy weight calculator anchors its estimate in official breed standard ranges instead of a single formula, then adjusts using your puppy's current weight.

Why week-by-week percentile charts belong with your vet

You may see puppy growth charts online claiming to show the exact percentage of adult weight a puppy has reached at every week, broken down by size. Treat those with caution. The two primary sources that would contain that data, Salt et al. 2017 and the WALTHAM growth charts built from the same dataset, publish their growth curves only as chart images, not as a text table anyone can look up. A site claiming to reproduce that exact week-by-week table is going further than the published research supports.

What the WALTHAM charts are built for instead is centile tracking done by a vet: three or more weight measurements over time, plotted against which percentile line your puppy is tracking, then projected forward to where it's expected to flatten out. That reflects your puppy's own growth pattern, not a breed average, but it needs repeated weigh-ins and the chart itself, which is why it belongs with your vet rather than a calculator page.

FAQ

At what age is a dog considered fully grown?

It depends on size. Small and medium breeds are usually fully grown by 10 to 12 months old. Large and giant breeds take longer, typically 18 to 24 months, per the MSD Veterinary Manual, VCA Animal Hospitals, and the Purina Institute.

Do small dogs stop growing before large dogs?

Yes. Toy breed puppies reach roughly 50% of adult weight by about 12 weeks old, while giant breed puppies don't hit that halfway point until roughly 26 weeks, per a calculator site drawing on the Hawthorne 2004 study (calculatorsfordogs.com). Small and medium breeds finish growing entirely by 10 to 12 months; large and giant breeds keep growing for another 6 to 12 months beyond that.

Can I tell how big my puppy will get from its current weight?

Roughly, yes, though every simple formula has limits. Doubling weight at 4 months gives a fast estimate but ignores breed-size differences. Dividing current weight by current age in weeks and multiplying by 52 assumes growth is a straight line, which is not true for large and giant breeds. The puppy weight calculator starts from your breed's official adult weight standard instead, then adjusts from there.

What are growth plates, and when do they close?

Growth plates are areas of developing cartilage near the ends of a dog's long bones. While they're open, the bone can still get longer. They close and convert to solid bone once a dog reaches skeletal maturity, which the MSD Veterinary Manual puts at 8 to 12 months for small and medium breeds and 10 to 16 months for large and giant breeds.

DogTally guides and tools are for information only and are not veterinary advice. Talk to your vet about your dog's health.