Different dogs take longer to grow than others. Generally, the size of the breed determines how long it takes for the puppy to be full-grown. A toy puppy, for example, will be full-grown at a year. A larger breed, such as a retriever, will be full-grown at two years. It all depends on the size of the dog, but most dogs are fully grown by two years old.
If you have a mixed breed or mid sized dog, it might be difficult to determine when it is fully grown. Usually, by one year, a dog may still act like a puppy and get into trouble here and there, but for the most part, they are through with using your house like a toilet. By a year old, a dog should be using the designated bathroom spot in which to do his business, no matter what size breed.
A larger breed dog may still jump and act like a little puppy. This can be a problem because he will be big in size but small in brain. He will still think like a puppy but with the body of a dog. It is important to train the puppy and make sure that he is not only going to the bathroom in the designated spot, but also able to behave himself around humans.
No one wants a dog jumping all over them the minute they walk in a door, no matter how much they love animals. A big dog can cause a lot of problems and can actually knock people down. This is why it is important to start puppy training as soon as you bring your puppy home.
Understand now that it will take a year before your puppy can be trusted to be around the house and not have an accident. However, even when fully grown, your puppy will have the mentality of a two year old child. They will be able to understand simple commands and respond well to love and affection.
When your puppy gets older, he or she will calm down a bit and not seem so “hyper.” You do have to also do some research on the breed to determine how highly strung the breed normally is. Some dogs are always going to be rather highly strung and others will be relaxed. Pure bred dogs are usually a lot more maintenance and higher strung than mixed breed dogs.
If you adopt a puppy from the pound and are not sure if he is full grown, you will usually be able to tell by his actions as well as some physical characteristics. Puppies lose baby teeth just like humans, so if you take a look in the mouth of the puppy, you should see adult sized canines. This will give you an indication that the puppy is or close to being full grown.
There are other characteristics, too. A female dog will grow nipples and become able to breed at six months. Male dogs will begin humping different objects at about six months to a year. This is a sign your dog is actually a teenager and about to enter adulthood. If the animal has been spayed or neutered, you will not be able to determine the age of the dog by this characteristic.
Rule of thumb is that a small dog will be considered full grown at one year old and a larger dog generally by two.