No matter how old your dog gets, he’ll always be your puppy. You might wish you could freeze time and keep your dog small forever. But, alas, puppies grow up—and fast! If you have a young dog—especially a mixed breed—it can be hard to know when he’s reached his mature size. So, how can you tell when a puppy will stop growing?

First off, it’s important to understand why predicting your dog's final size is valuable. Maybe you want to purchase a crate or splurge on a fancy bed or collar that you don’t want your dog to grow out of. Knowing your dog’s full size is also critical when deciding their diet or planning out how much exercise they’ll need.

In reality, the age at which your pup stops growing depends on his size. Small dogs and giant breeds mature at different rates. We’ll break it down below.

Toy to Medium Sized Dogs

Tiny dogs can reach full maturity months or even years before larger dogs stop growing. Toy breeds, like Chihuahuas or Pomeranians, will reach full size at around 8-12 months. Small-Medium breeds, like Beagles or Corgis, will follow a similar time frame.

Medium to Large Breeds

Medium-Large Breeds like Collies, Labs, or Golden Retrievers will reach their final height and weight around 10-16 months.

Giant Breeds

The biggest dog breeds, like Great Danes or Bernese Mountain Dogs, can reach their full size anywhere between 10-16 months old. Some may even continue to fill out for up to 18 months.

Mystery Breeds

The above rules are great if you know your dog’s breed. But what about mixed breeds or dogs whose backgrounds are a total mystery?

If you know the dog’s background, you can predict his size a little easier. Typically your dog’s female parent will have more influence on his final size.

If you have no information about the dog’s history, you can only make some rough guesses. A dog with giant puppy paws will certainly not grow into a teacup pup, just as a dog with dainty legs won’t end up with a weight that those little legs can’t support. And while it’s no exact science, you can try to guess your dog’s final size by doubling their weight at 4 months old (for giant breeds, double their weight at 5 months.)

Regardless of breed, your puppy will be very busy during this growing period. On top of reaching their full height and weight, they’ll also be busy growing out their adult coats, learning constantly, and burning lots and lots of energy. Nutrition is very important for a developing puppy. Check in with your vet for advice on feeding a growing dog—each dog has specific needs and both underfeeding and overfeeding can be detrimental.

There’s no joy in the world like watching your puppy grow up into a full-fledged dog. Understanding just how big he’ll grow can help you plan for his every need—from food and yard space, to just how big a lap he’ll need to curl up in.