Over the first year of their life, your puppy will undergo significant changes in their size, shape, and behavior. Understanding the key stages of growth will help you know what to expect at different times in their early years and prepare in the right way.
One important thing to note is the difference in the first few years between small breed and large breed dogs. Depending on the sort of dog you have—along with their sex and their parents—growth will happen at a different pace, and there are different things to look out for.
The first three to four weeks of your puppy's life
The first 14 days after your puppy is born are a crucial time to make sure they progress into healthy adulthood. It's important to look after them carefully in the first 48 hours, and make sure they get the heat and nutrition they need. This includes colostrum, which puppies get from suckling their mother, as it helps support their immune system. Between days nine and 13, your puppy's weight will also double—so if they seem to be struggling to put on weight you may wish to consult a vet.
One month into their life
During the first month, your pup's first teeth will appear, but their jaw and tooth strength are still relatively weak. Between 25 and 30 days, their weight will multiply by four, and the first hairs they had will begin to shed and be replaced by their "real" fur. They're not yet at their "growth spurt" stage, but it's essential to start as you mean to go on with a nutritionally appropriate weaning food.
All dogs, whatever their breed, have an "immunity gap" between four to 12 weeks where they are susceptible to illness. This is because they've stopped feeding on their mother's milk—which transmits immune support—but their bodies aren't yet able to develop their own immunity. In this stage, keep a close eye for any signs of sickness.
Your puppy at three to five months
At this point, your puppy will be growing fairly rapidly whether they're a small or large breed. By five months, large breed dogs will have developed the skeletal structure they need for adulthood and be half their adult weight. They will also have at least double the nutritional requirements of an adult dog! Small dogs will be going through their most intense growth period and you can stop rehydrating their food—give them a larger kibble which helps them chew and develop good dental hygiene for their new teeth.