When do puppies stop growing?

The short version, by size

The American Kennel Club’s chief veterinarian puts it simply: small breeds are mostly done growing by about 6 to 8 months, medium breeds by around 12 months, and giant breeds by 12 to 18 months, with the very largest (Mastiffs are the AKC’s example) taking up to about 24 months. The same AKC article shows small dogs at roughly three quarters of their adult size at 6 months and at full size by 12 months, so “done by 6 to 8 months” means the fast part is over, not that the scale stops moving.

That pattern matches the research. In a long-term study of Labradors, Newfoundlands and two other large breeds raised in ordinary homes, Trangerud and colleagues found that female Labradors reached mature weight at about 351 days (a little over 11 months) and male Newfoundlands at about 413 days (about 13.5 months). Bigger dogs grow for longer because they have more growing to do.

Read the table as a range, not a deadline. A puppy at the fast end of its class can be near adult weight a couple of months before one at the slow end, and both can be perfectly healthy.

Why weight keeps going up after height stops

Height is set by the growth plates, soft zones of cartilage near the ends of the long bones. Once they harden and close, the legs stop getting longer. The AKC notes that dogs keep adding muscle and some body fat after that point, which is why a 10-month-old Labrador can look tall enough but still gain a few pounds before its second birthday.

This is also why growth charts for dogs are built on weight rather than height. The WALTHAM puppy growth charts and the Salt 2017 growth standards published in PLOS ONE both track body weight against age, from 12 weeks to 2 years in the Salt study. Salt and colleagues built their charts from about 158,000 weight records of roughly 50,000 dogs seen at Banfield clinics, but they did not produce a chart for dogs over 40 kg (about 88 lb), so the giant breeds are the least well mapped.

How to tell where your puppy is

1. Weigh your puppy on the same scale every 2 to 4 weeks until 6 months, then every 1 to 3 months. That is the rhythm WALTHAM suggests.
2. Enter the weights in the puppy growth chart. It draws the expected curve for your dog’s size class and shows where each weight falls.
3. Look at the shape, not one point. A puppy that tracks along its own curve is doing what it should, even if that curve sits above or below the middle line.
4. If you know the breed, compare with a breed chart such as the Labrador Retriever or Golden Retriever page.

Large and giant breeds: go easy on hard exercise

Because their growth plates stay open longer, the AKC suggests holding off on jogging and long runs on hard surfaces until roughly 14 to 18 months for large and giant breeds. Short walks and play on grass are fine. Ask your vet before starting running or dog sports, since they can judge your dog’s joints in person.

What the numbers can’t tell you

Mixed-breed puppies, rescues with an unknown birthday, and dogs whose parents were very different sizes are harder to place in a class. In those cases, the best estimate comes from a few weights over time, not a guess at the breed. The puppy weight calculator turns one current weight into a likely adult range, and the range gets tighter as your puppy gets older.