Knowing what to expect as your puppy grows up will help you prepare for his training and exercise needs. Below is a guide to your new puppy's growth, both physical and mental. This is only a guide and is not set in stone, as there are differences among breeds and individuals.
From birth – 12 days: Neonatal Period
The puppies are completely dependent on the care of their dam. Their eyes and ears are sealed, but they can smell and feel.
13 – 20 days: Transitional Period
Puppies' eyes and ears begin to open, though the eyes are not fully functional until 10 weeks old.
3 - 8 weeks:
Baby teeth are coming in. Ouch!
3 - 14 weeks: Critical Socialization Period
This is the most important developmental period for you to be aware of. This is a time of immense learning. Puppies are extremely impressionable and are learning what is safe and normal in their world. This is when puppies must have safe, positive interactions with a variety of new people, new dogs, and other animals in order to be social as adults. They are learning bite inhibition and social skills from other dogs as they play. They must also have positive exposure to novel stimuli such as various sights, sounds, smells, surfaces. They can begin learning obedience foundation such as sit, down, and come (in 1-2 minute training sessions). They should be learning to accept handling, being held, and having nails trimmed. Potty training should be well underway, as the puppy is already developing a preference for where he will potty (hopefully not on carpet!). Researchers Scott & Fuller found that puppies who had not seen a stranger before 7 weeks old are unlikely to approach one without encouragement. If they have not seen one before 14 weeks old, they may never voluntarily approach strangers. Read more about safe puppy socialization here.
Between 8 - 11 weeks: First Impact Period (“fear period”)
Within the Critical Socialization Period, there is usually a brief “fear period.” It may last a few days or a week. Your normally confident, curious puppy may hesitate around new stimuli, and even around things that didn't bother him before. Socialization can be scaled back but should continue, with extra care taken to prevent negative experiences from traumatizing him. Then your puppy will return to his usual curiosity about the world.
3 - 8 months:
Adult teeth are replacing baby teeth. Give lots of toys and chews!
4 - 8 months: Flight Instinct Period
This oddly-named period is when your “puppy” starts to be more grown up. He will be ready to leave the security of home and family and be much more interested in exploring the big wide world, and especially in interacting with other dogs. He will experiment with new behaviors, and often issues with marking, counter-surfing, barking, pulling on leash, and not coming when called pop up.
Between 6 - 15 months: Second Impact Period (“fear period”)
The second “fear period” is not as well-defined. It may last a few weeks to several months, and the onset may be gradual or sudden. Avoid forcing your dog into scary situations. Instead, help him gain confidence by encouraging investigation and rewarding good choices. Continue careful socialization. Beware of dog parks.
Between 9 - 18 months: Growth plates close
Growth plates are open areas between bones that are particularly susceptible to injury. Hard impacts that occur before the growth plates finish growing (“close”) can affect bone growth and cause permanent injury. This is why young dogs should not be exposed to repetitive or hard impact exercise such as jumping, jogging (especially on paved roads), or catching frisbees. Spaying/neutering before the growth plates close also impacts the dog's physical development. X-rays can confirm when an individual dog’s growth plates are closed, but rules of thumb are:
Small dogs (<20 lbs): 6-8 months
Medium dogs (21-50 lbs): 12 months
Large dogs (51-100 lbs): 12-18 months
X-Large dogs (100+ lbs): 24 months
2 - 3 years: Maturity
Dogs are often considered “adult” around 1 - 1.5 years, but full maturity, both mentally and physically, is around 2 - 3 years. Finally!