Life stages
When is a dog considered an adult?
Your vet, your trainer and the food label may each give a different answer, and all of them can be right. This page untangles physical, sexual and social maturity, explains why size changes the timeline, and covers what shifts in food, exercise and training as your dog moves into adulthood.
Three kinds of adult
Adult means three things: fully grown, sexually mature and socially mature
Physical maturity is the easiest to see: the dog stops growing and its growth plates close. Sexual maturity comes with puberty, which Naomi Harvey's 2021 review places between about 6 and 9 months in males and 6 and 16 months in females. Social and behavioral maturity is the slowest of the three, and the review puts it between 12 and 24 months, while noting that the timing by breed is still a considerably under-researched question.
AAHA's 2019 Canine Life Stage Guidelines tie the stages together. A puppy is a puppy from birth until rapid growth stops, around 6 to 9 months depending on breed and size. A young adult runs from there until physical and social maturation is complete, which the guidelines say happens in most dogs by 3 to 4 years. Mature adulthood follows, and the senior stage starts in the last quarter of a dog's expected lifespan.
- Physical: growth stops and the growth plates close
- Sexual: puberty, from about 6 to 16 months
- Social: settled adult behavior, from about 12 to 24 months
- AAHA's young adult stage: complete by 3 to 4 years in most dogs
Size and growth
Small dogs finish growing by about 8 months; giants can take two years
Size changes the physical timeline more than anything else. An AKC article quoting the club's chief veterinarian, Dr. Jerry Klein, says small breeds typically stop growing by 6 to 8 months and medium breeds reach adult size at about 12 months. Large and giant breeds are still growing at 12 to 18 months, and very large dogs such as Mastiffs may take up to 24 months. Growth ends when the growth plates harden and close, which marks the bone reaching its final size.
Two practical rules follow from that. The AKC says puppy formulas are typically fed until around 11 to 14 months, so ask your vet when your dog should switch rather than going by the birthday. And it says jogging and road work should wait until the growth plates have fused, at about 14 to 18 months, with the most caution for large and giant breeds; short walks on grass are the safer choice until then.
| Size | Adult size reached, per the AKC |
|---|---|
| Small | About 6 to 8 months |
| Medium | About 12 months |
| Large | Still developing until 18 to 24 months |
| Giant | 12 to 18 months, and up to 24 for the biggest, such as Mastiffs |
Big dogs
Big dogs stay adolescent longer because body and brain both finish late
A Great Dane at 18 months can look fully grown and still behave like a teenager, and the timelines explain why. Its skeleton may still be developing into the second year, social maturity is still under way, and in females the first heat can come late: AAHA notes that the age of first heat ranges from 4 months in some small breeds to 24 months in some large ones. Put together, it is no surprise when a big dog's adolescence runs to 2 or 3 years.
Training follows the same slow curve. In Lisa Wallis's 2020 study of 1,207 adult dogs, owners rated responsiveness to training highest between 3 and 6 years, and activity and excitability kept falling with age. The study did not compare sizes, so read it as the general pattern rather than a rule for your breed: the steadiness people mean by adult usually arrives some time after the second birthday, not on it.
What changes
Adulthood changes the food, the exercise and the training plan
Moving a dog into adult routines is a series of small changes, not a single switch. AAHA's guidelines organize vet care around the life stages, so the young adult years are a good time to set a health baseline with your vet. Training shifts too: the basics a puppy learned need proofing in harder places, and an adolescent that seems to have forgotten them is usually still maturing rather than slipping backward.
Daycare changes with age as well. A young puppy usually starts on half days at $33, and once a dog is grown a full day at $42 or a full-day 10-pack at $380 often fits better. Every dog starts with the free evaluation on a weekday between 6:30 and 9:30 AM, where an intact adolescent's playgroup placement is also decided. In Gloucester the dog license comes from the City Clerk at 9 Dale Ave and needs a current rabies certificate.
- 01
Ask your vet when to move from puppy food to adult food, rather than switching on a birthday.
- 02
Ask before starting runs, jogging or long hikes, especially with a large or giant breed.
- 03
Keep vaccines and boosters on your vet's schedule as your dog moves into adulthood.
- 04
Raise training difficulty gradually: new places first, then distance, then distractions.
- 05
Review daycare length as stamina grows, from half days toward full days.
- 06
Renew the dog license every year; Gloucester licenses are due by April 30.
At Dogtown
Training through the late teens: Calm & Connected and the adult programs
Calm & Connected is our program for adolescents, new rescues and adult dogs, in blocks of 4, 6 or 8 weeks, working on impulse control, minor leash reactivity, handling and real-world reliability. Our adolescent dog training page sets out how it runs. Gabriella Pope, our Director of Training & Canine Behaviorist, leads it with positive reinforcement only, sessions start from $94, and the two-week Advanced board and train is written for adolescent dogs who need real-world reliability.
When your dog is ready for an adult milestone, Canine Citizen Academy prepares adolescents and adults for the AKC Canine Good Citizen test, with an emphasis on dependable manners in public. On Cape Ann the off-season beaches make a good final exam for a young adult's recall, from October 1 at Good Harbor on even-numbered days and Wingaersheek on odd ones, at the time of writing; keep a long line on until it holds. We reply to the training form within one hour on business days.
- Calm & Connected: 4, 6 or 8 weeks for adolescents and adults
- Advanced board and train: two weeks of real-world reliability
- Canine Citizen Academy: preparation for the AKC Canine Good Citizen test
- Private sessions from $94 for one specific goal
At Dogtown
Training for the teenage years and beyond
Adolescent and adult programs led by Gabriella Pope, plus daycare that grows with your dog.
Asked and answered
Questions people ask about this
Short, complete answers you can act on today. More in the full FAQ.
Is a one-year-old dog an adult?
When should I switch my dog to adult food?
When can my large-breed dog start running with me?
Why does my two-year-old dog still act like a puppy?
Does a dog's adult age depend on its breed?
More questions? Read the full FAQ
Sources
- AKC: when does my puppy finish growing?
- AAHA: 2019 canine life stage guidelines
- Harvey (2021), Frontiers in Veterinary Science: how old is my dog?
- Wallis, Szabo and Kubinyi (2020), Frontiers in Veterinary Science: age differences in canine personality traits
- AKC Canine Good Citizen
- City of Gloucester: dog licensing
- City of Gloucester: beach information
Rules and dates change. We re-check every beach, licensing and ordinance page each spring and fall; the source above is the current word.
Keep reading
Next step
Training for the young adult years
Send the training form with your dog's age and what has changed lately. We reply within one hour on business days.
- 01Free evaluationWeekdays 6:30 – 9:30 AM
- 02Book a dayOnline, in the app or by phone
- 03Play, rest, repeatReport card at pick-up
