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mastiff puppy with larger dog

This pup has a LOT of growing to do

The essentials

  • The amount of time dog’s take to reach adult size varies — It can take anywhere from 6 to 24 months of age.
  • Large breed dogs tend to take longer to finish growing — Since they have larger bones, they need more time to grow.
  • If you don’t know your dog’s breed, there are ways to estimate their adult size — Loose skin and growth plate appearance can be good indicators.

How puppies grow

Different breeds of dogs have different growth rates, so there isn’t a universal age at which puppies stop growing. Even if your dog is considered to be an “adult,” by age (1.5 years old for small breeds, 1.5 to 2 years old for larger dogs), they may still continue to grow physically. Just like humans, growth stages are determined by skeletal development.

Growth plates are soft areas of tissue located at the ends of long bones, like the bones in puppies’ legs. Throughout puppyhood, the growth plates produce tissue, which hardens into bone as your dog matures. When your dog reaches their adult height, the growth plates will be completely hardened.

In general, larger breeds take longer to reach their full size, simply because their bones are much larger than small dogs’ bones. Even when skeletal development is finished, your dog still may change in size as they accumulate more muscle and fat.

Small breeds

Small dogs under 25 pounds, such as Chihuahuas and beagles, will usually finish growing in less than a year. Some especially small breed dogs, like toy breeds, can finish growing in as quickly as six months.

Medium breeds

Dogs of medium adult size, like border collies and Fox red Labrador retrievers, usually finish growing around one year, give or take a few months.

Large breeds

Longer bones need more time to grow to their final height, so larger breeds and giant breed dogs can take anywhere from a year to two years to finish growing, depending on the breed and final size. For Great Danes and other giant breeds, it’s not uncommon to grow for a full two years before reaching full growth.

Stages of physical development in puppies

In the first year of your new puppy’s life, it may seem that they’re changing every day. Here are a few of the most important physical milestones and their associated weeks of age.

Birth: From birth until 8 weeks, your puppy will be working on becoming a self-sufficient creature. Eyes and ears will open, they will start to make sounds, they will wean off of their mother’s milk, and they will gradually sleep less and less. Puppies will usually become more adventurous with age.

8 weeks: This is usually when puppies can leave the breeder and go home with their owners. At this point, they will be developed enough to run, play, and eat puppy food. They will also have baby teeth.

8 to 12 weeks: Puppies usually experience a growth spurt during this period. Biting and chewing on everything is normal during this age.

4 to 5 months: At this point, the adult coat will likely start growing in and baby teeth will start falling out.

6 to 9 months: Six months often marks the transition to sexual maturity for dogs, which is why neutering or spaying around this age is standard. Female dogs will likely go into heat for the first time around six months. Within this period, your dog should gain all of its adult teeth. Smaller-breed puppies, like dachshunds, may finish growing at this point.

9 to 12 months: Unless you have a big dog, it’s likely that your dog is just about done growing at this point. Neutering your dog will slow growth.

2 years: Even though most dogs will be done growing around 1 to 1.5 years old, reaching mental maturity can take up to two years. So don’t fear if your dog still acts like a puppy for a while after they’ve finished growing.

How to estimate the size of a mixed-breed dog

If you have a purebred puppy, finding out their adult size is easy: simply contact the breeder. But what about when you have a mixed-breed dog or when you don’t know the breed? The truth is, you’ll have to estimate.

If you know the breed or parents:

If you’ve purchased the dog from a breeder, chances are you will be able to take a look at the parents. This is usually a pretty good indicator of a dog’s adult weight and size. Even if you don’t know what the parents look like, information about breed size and weight should be easy to find. Keep in mind that male dogs are usually slightly larger.

Use the AKC’s standard breed weight chart to get a rough idea of your pup’s adult weight.

If you don’t know the breed or parents:

If you rescue your dog or aren’t sure about the breed, there are some physical indicators that can help you estimate its adult size. Keep in mind that every dog is different and these are all techniques designed to help you guess.

  • Gauge the amount of loose skin — While some dogs, like American bulldogs, are simply wrinkly, loose skin is often an indicator that your dog has room to grow.
  • Feel the ribs for growth plates — If you run your hands down a puppy’s rib cage, you may be able to feel knobs along the edge of the bones, which are the growth plates that are still hardening. While this won’t predict the adult size, there’s a good chance your dog still has some growing to do if you can feel these.
  • Get a canine DNA testing service — If your dog’s bloodline is a little bit hazy, you can purchase canine DNA testing kits to help you get a better idea. You can then look up your dog’s breed(s) to predict how large they will get. However, some veterinarians are wary of the lack of standards and the potential lack of accuracy delivered by these kits.

Are paws a good indicator of adult size?

Paw size sometimes correlates with adult size, but it’s not a reliable way to predict how large your dog will get. Especially when puppies are young, it’s common for paws to look disproportionately large or small.

How to support your dog’s growth: Diet and exercise

To support healthy growth in your puppy, it’s important that they are taking in and exerting the proper amount of energy. Because they grow so rapidly, puppies need more calories than adult dogs. Check out our guide to feeding your puppy for tips and more information on choosing a dog food that supports your puppy’s growth.

It’s also important to foster the appropriate amount of exercise at each stage of development. For example, even active breeds of dogs don’t need formal walking before they’re four months old. Playtime in the house should be plenty of exercise for a young puppy. As they age, however, follow your veterinarian’s advice for daily exercise.