When My Puppy Becomes An Adult?

by Marie Jones

There’s nothing quite like the joy that comes from seeing your healthy, full-of-life puppy grow into a healthy, happy adult dog. And of course, as your dog grows, its nutritional needs change.

The amount of food, and the specific combination of vitamins and minerals, that a growing puppy needs differ quite considerably to those needed by a busy adult dog, as well as by a less active senior dog.

It’s why Billy + Margot®is focused on offering balanced nutrition – and different products - for your dog at each life stage.

However, all breeds are different, and knowing exactly when your puppy becomes an adult can be tricky.

Here’s a quick guide:


Toy breed and small breed puppies grow very quickly, typically reaching full physical maturity at about nine to ten months of age. They need a very high food intake as a pup – three times as much energy as an adult dog of an equivalent weight in the post-weaning period, reducing to twice as much as they mature to their adult size - to provide sufficient energy, protein, fat, vitamins and minerals to support this rapid growth.

The average life expectancy of small breed dogs is several years longer than that of larger breeds. Because of their longer life spans, these breeds spend the majority of their lifespans as adult and senior dogs.


Medium breeds are those which weigh between approximately 20 to 50lbs as adult dogs. They grow at an intermediate rate between small and large breeds and reach maturity at around 12 months of age. Likewise, their nutritional needs during puppyhood fall between that of a small and large breed dog.

The essential fatty acids DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) are two nutrients critical for all sizes of pups, from a tiny chihuahua, to a medium sized spaniel, to a giant Great Dane. These omega 3 fatty acids are critical for normal brain, eyes and ears development in pups and facilitate much easier trainability.


Large and giant breeds reach maturity later than smaller breeds and may not be classified a fully grown adult dog until around 18-24 months. During their development period, large breed pups require a diet that supports controlled and steady growth. It is critical that young large breed dogs between weaning and two years old get the balanced nutrition they need, without excess calories, in order to prevent excessive growth rates, which may lead to developmental abnormalities in the bones and joints. Ideal levels of protein and fat can help balance growth in large-breed puppies and the diet for a large breed puppy should be less energy-dense than the diet for a smaller pup.

Quality, natural meat-based proteins provide the right balance of critical amino acids to help with lean muscle development, immunity and promote healthy digestion. Appropriate calcium and phosphorus levels are vital for all pups, but are particularly critical in larger breed pups tol help support optimal bone strength and growth. One very important thing to remember in feeding all pups is that a roly poly puppy is not ideal! Keep them lean during puppyhood, as pups which are overweight are predisposed to being overweight as adult dogs.

Want to know more about what to feed your dog?