By the PupGauge editorial team · Last reviewed October 2026 · Based on published veterinary research (see sources) and our methodology. General information, not veterinary advice.
Quick answer
Puppies move through five stages: neonatal (0–2 weeks), transitional (2–4 weeks), socialisation (about 3–12 weeks), juvenile (3–6 months) and adolescence (6 months to about 18 months or longer). The socialisation window is the most important stage for lifelong behaviour.
Planning a litter or a new puppy? See the dog pregnancy calculator, the puppy feeding calculator and the crate size calculator.
A puppy changes faster in its first year than at any other time of life. In a few months it goes from blind and deaf to running, teething, testing boundaries and finally settling into adulthood. Knowing what is normal at each stage helps you spot problems early, plan training at the right time and keep growth on track.
Puppy Development at a Glance
| Stage | Age | Key milestones |
|---|---|---|
| Neonatal | 0–2 weeks | Eyes and ears closed; sleeps and feeds; birth weight often roughly doubles in the first week to ten days |
| Transitional | 2–4 weeks | Eyes open (about 10–14 days); ears open; first wobbly steps; first teeth appear |
| Socialisation | About 3–12 weeks | Play, curiosity, learning from littermates and people; weaning |
| Juvenile | 3–6 months | Rapid growth; teething; learning basic training |
| Adolescence | 6–18+ months | Sexual maturity; testing limits; growth slows; adult coat |
Neonatal Stage: Birth to 2 Weeks
Newborn puppies cannot see, hear or regulate their own body temperature well, so they depend entirely on their mother for warmth and milk. Breeders weigh puppies daily at this age: steady gain is the best sign that a puppy is feeding well, and a puppy that loses weight needs prompt veterinary attention.
Transitional Stage: 2 to 4 Weeks
Eyes usually open at around 10–14 days and ears soon after. Puppies begin to stand, walk and react to sounds. The first puppy teeth appear at about three weeks, and many litters start trying soft food around 3–4 weeks as weaning begins.
Socialisation Period: About 3 to 12 Weeks
This is the window when puppies learn most easily that people, other animals, sounds and places are safe. Positive, gentle experiences now shape behaviour for life. Veterinary behaviour organisations advise starting careful socialisation before the vaccination course is complete, choosing safe places and healthy, vaccinated dogs, because the risk from missed socialisation is high. Most puppies go to new homes at about 8 weeks, after weaning is complete. Many trainers describe a short “fear period” during this window, when a puppy may react more strongly to frightening events, so keep new experiences calm and positive.
Juvenile Stage: 3 to 6 Months
Growth is fast. Most puppies gain weight every week, and large breeds can gain several kilograms a month. Adult teeth replace puppy teeth from about 3–6 months, so chewing peaks; give safe chew toys and redirect from furniture. This is an excellent time for basic training such as recall, sit and loose-lead walking. Track weight against the puppy weight chart and adjust food using our puppy feeding guide.
Adolescence: 6 to 18 Months and Beyond
Many dogs become sexually mature in this period, small breeds earlier than large ones. Adolescent dogs may seem to forget training, push boundaries and become more independent. That is normal and passes with consistent, patient training. Growth slows and stops at different ages by size, from about 9–12 months in small dogs to as late as 24 months in giant breeds (see when dogs stop growing). Large breeds need careful feeding and exercise throughout (see growing a large-breed puppy safely).
Planning tip: Write down your puppy’s birth date and weigh it every two weeks. Enter the weights in the Puppy Weight Calculator to see the likely adult range and to spot a stalled or unusually fast curve early.
Typical Vet Milestones
- First weeks at home: health check, vaccination plan and parasite control set by your vet.
- Through the vaccination course: follow your vet’s schedule, which depends on local disease risks.
- Around adolescence: discuss spay or neuter timing, which can depend on breed size.
- About 12 months: review food, weight and body condition as your dog approaches adulthood.
When to Call the Vet
Contact your vet if a puppy stops gaining weight, refuses food for more than a day, has repeated vomiting or diarrhoea, seems lethargic, or limps. Young puppies can become unwell quickly.
Frequently Asked Questions
When do puppies open their eyes?
Usually at around 10–14 days old, with full vision developing over the following weeks.
What is the most important stage of puppy development?
The socialisation period, from about 3 to 12 weeks, has the biggest lasting effect on behaviour. Gentle, positive exposure to people, sounds and places during this time is important.
When do puppies start teething?
Puppy teeth appear at about 3 weeks. Adult teeth replace them between roughly 3 and 6 months, which is when chewing is most intense.
At what age is a puppy an adolescent?
From about 6 months, lasting until roughly 18 months or longer in large breeds.
When is a puppy considered an adult?
When it reaches adult size, from about 9–12 months for small dogs to about 18–24 months for giant breeds.
Related Guides and Calculators
- How Much to Feed a Puppy – calories and meals by age.
- When Do Dogs Stop Growing? – growth timelines by size.
- How Big Will My Puppy Get? – adult size estimates.
- How to Tell a Dog’s Age by Its Teeth – dental age timeline.
- Dog Life Stages Explained – care for every age.
Sources and Method
Developmental stages follow widely used veterinary and behavioural descriptions, including the 2019 AAHA Canine Life Stage Guidelines and the American Veterinary Society of Animal Behavior position statement on puppy socialisation. Growth timings follow Hawthorne et al. (2004). Figures are typical ranges for healthy dogs, and individual dogs vary. How PupGauge builds its estimates is explained on the methodology page. For advice about your own dog, speak with your veterinarian.