When do puppies stop growing? Ages by adult size

Three sources, three ways to define “done”

The sources agree on the shape — small dogs finish first, giants last — but they measure the finish line differently, so their ages don’t match exactly.

• The 2004 kennel study (Hawthorne and colleagues) fitted a growth curve to each of 12 breeds, from Papillon to English Mastiff, and reported the age at which each breed reached 99% of its adult weight. It found about 9 to 10 months for toy, small and medium breeds and about 11 to 15 months for large and giant breeds. The dogs lived at a research center, were fed to keep an optimum body composition and were weighed weekly; some breeds were represented by only a handful of puppies.
• The Merck Veterinary Manual says growth begins to plateau after 6 months and that growth and skeletal maturity may be complete by 8 to 12 months in small and medium breeds, but not until 10 to 16 months in large and giant breeds.
• The U.S. pet data (Salt and colleagues, 2017) defines adult weight as each dog’s own median weight at 2 to 3 years. In this data the typical dog at 18 months still weighs only 93% to 95% of that, so puppies take longer to reach 90% or 95% than in a study that measures to a growth curve’s plateau.

None of these is wrong. A kennel puppy fed for an optimum body composition, a pet puppy weighed at routine vet visits and a textbook summary simply answer slightly different questions.

Ages by size class in the U.S. data

Here is when the typical (median) puppy in each size class reached half, three-quarters, 90% and 95% of its adult weight in our summary of the 2017 study data. Size classes are by expected adult weight, as in the study.

Two things stand out. First, the halfway point really does arrive earlier in small dogs: 16 weeks for class I against 22 weeks for class VI. Second, the smallest dogs are not the first to reach 90% in this data. Because adult weight here is the weight at 2 to 3 years, any weight a toy dog adds after its first birthday counts toward these milestones, and weights alone can’t tell frame growth from adult weight gain. Read the late milestones for small dogs loosely.

What the kennel study found, breed by breed

The 2004 study’s ages at 99% of adult weight spread from about 9 months to 15 months. A few examples, with the paper’s weeks converted to months:

• Papillon: 41.7 weeks (9.6 months)
• Beagle: 41.9 weeks (9.6 months)
• Labrador Retriever: 52.1 weeks (12.0 months)
• Great Dane: 52.1 weeks (12.0 months)
• English Mastiff: 65.2 weeks (15.0 months)

The Labrador and the Great Dane landing on the same age is a useful warning against simple size rules: within the large and giant group, breed matters. The authors also note that earlier studies found males taking longer than females to reach adulthood.

A separate 2007 study of 700 dogs of four large and giant breeds raised in homes (Newfoundland, Labrador Retriever, Leonberger and Irish Wolfhound) fitted a different growth curve and reported maturity between 351 days (female Labradors) and 413 days (male Newfoundlands) — about 11½ to 13½ months. We read only its abstract, so we don’t know exactly how it defined maturity.

Is my 7-month-old done growing?

Seven months is about 30 weeks. In the U.S. data, the typical puppy at that age has reached:

• about 76% of adult weight in class I and 79% in class II,
• about 75% in classes III and V and 76% in class IV,
• about 71% in class VI.

Individual puppies vary a lot around those medians. In class V, for example, 8 in 10 puppies at 7 months were between 62% and 88% of their adult weight. So a 50-lb (22.7-kg) male Labrador at 7 months has a central estimate of 66 lb as an adult, with a middle half of 61 to 72 lb. Roughly a quarter of his adult weight is still to come.

The practical answer for most 7-month-olds: growth is slowing, not over. Small and medium dogs are close to done by their first birthday; large and giant dogs keep gaining into their second year. Merck’s guidance to move a dog from a growth diet once it reaches about 90% of its expected adult weight falls, for large breeds, at around 46 to 50 weeks in this data — a conversation to have with your vet, covered in the guide to feeding a large-breed puppy.

Height, and a puppy that stops gaining

Height. All three sources measure weight, not height. Merck’s ranges describe skeletal maturity as well as growth, but we found no open dataset of puppy heights by age to give you numbers, so we don’t estimate height.

A puppy that stops gaining. A slower weekly gain after 6 months is expected. A puppy whose weight stays flat or drops well before its size class reaches 95% of adult weight is different, and worth a call to your vet. Our puppy growth chart flags exactly that pattern. It also flags a puppy that crosses two or more centile lines: in a 2020 follow-up study, fewer than 5% of healthy dogs crossed more than two lines while growing, but 49% of dogs that became underweight by 3 years had crossed two or more lines downward.

This is general information, not veterinary advice — talk to your vet if your puppy’s growth worries you.

Bottom line

For most puppies, “done” comes in stages. Half of adult weight arrives at 3½ to 5 months, three-quarters at 6½ to 8 months, 90% somewhere between 10½ and 14 months, and the last few percent can take until 16½ to 20 months in the U.S. data. The kennel study and Merck give earlier finish lines because they measure differently. To see where your own puppy is, enter its weight and age in the puppy weight calculator, which shows the share of adult weight reached so far, or read the full method in how big will my puppy get.