They don’t turn into dogs overnight, puppyhood fades one day at a time. Most dogs are physically full-grown by around their first birthday, though many large breeds keep filling out until 18 to 24 months. They become sexually mature much earlier, often from about six months, and they don't usually settle into calm, adult behaviour until closer to two years old. So your puppy is really three different ages at once, and that's completely normal.
That gap between growing up on the outside and growing up on the inside is where a lot of the confusion (and the chewed shoes) comes from. Below, we'll walk through each kind of maturity, what to expect from the first season, why the teenage phase is a real thing backed by research, and how to think about neutering. Everything here is meant to help you feel more prepared, not to replace a conversation with your vet.
The short answer
Dogs grow up in three overlapping ways, and they rarely line up:
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Physical maturity: when the body stops growing. Usually around 12 months for small and medium dogs, and 18 to 24 months for large and giant breeds.
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Sexual maturity: when a dog can reproduce. Often from about six months, sometimes earlier in males and later in big breeds.
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Emotional maturity: when the puppy brain finally settles. Commonly, around 18 months to two years.
Think of it this way: at six months, they might be able to father a litter, but they’re still just a youngster at heart, with plenty of growing left to do.
Keeping these three timelines separate makes the teenage months far easier to understand.
Physical maturity: when do puppies stop growing?
Every puppy grows at their own pace, but size plays the biggest part. As a rough guide:
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Small and toy breeds often reach their adult size by 8 to 12 months.
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Medium breeds tend to finish at around 12 months.
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Large and giant breeds can keep growing until 18 to 24 months.
The reason comes down to growth plates, the soft areas of developing tissue near the ends of the long bones. While they're still open, the bones are growing, and they gradually close once growth is complete. Bigger dogs have far more growing to do, so their plates stay open longer.
This matters for two everyday reasons. First, exercise: a young large-breed puppy's joints are still developing, so gentle, varied activity tends to suit them better than long runs or repetitive jumping while they're growing. Second, food. Growing puppies need a complete recipe made for their life stage, and big breeds in particular benefit from food designed with their size in mind. Our puppy food is made with freshly prepared meat as the main ingredient to support steady growth, and we have dedicated large breed and small breed recipes for dogs at either end of the scale.
Keeping your growing puppy slim and steady, rather than letting them shoot up quickly, is one of the kindest things you can do for their long-term joint health. If you're ever unsure whether your puppy is growing at the right rate, regular weight checks at your vet are a simple way to keep track.
Sexual maturity: when males and females grow up
Sexual maturity is the first big milestone, and it often catches new owners off guard when it comes sooner than expected.
Male dogs can become fertile from as young as five to six months, though it varies with breed and size. Signs that a male is maturing include cocking his leg to wee, marking territory, and showing more interest in females. Some males also start mounting toys, furniture or legs, which is usually a phase you can gently redirect with distraction and consistent training rather than telling off.
Female dogs reach sexual maturity when they have their first season. This can happen any time from around six months in smaller breeds, while some larger breeds may not start until they're over a year old (Royal Kennel Club). That first season is the clearest sign your dog is now physically able to have puppies, even though she is nowhere near emotionally ready to cope with them.
Because sexual maturity arrives while your dog still looks and acts like a puppy, it's worth being mindful when you're out and about. An unneutered male and a female in season can find each other from a surprising distance, so a bit of awareness during these months goes a long way.
Your dog's first season: what to expect
If you have a female who isn't neutered, knowing the rhythm of her seasons helps you support her and avoid an unplanned litter. A season lasts around three weeks on average, and after the first one, most dogs come into season roughly every six to seven months, though younger dogs can be irregular to begin with (Royal Kennel Club).
The cycle has four stages:
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Proestrus (around 9 days): the vulva swells, and there's a bloody discharge. Males take interest, but she usually isn't receptive yet.
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Oestrus (a few days): this is when she's fertile and willing to mate. The discharge often becomes lighter and more straw-coloured.
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Dioestrus: her body winds down from the fertile phase, whether or not she's pregnant.
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Anoestrus: the resting period before the next cycle begins.
Common signs she's in season include a swollen vulva, a bloody then pinkish discharge, licking the area more, weeing more often, and changes in mood such as being clingier or more restless. Some dogs also experience a false pregnancy afterwards, where hormone changes lead them to act as if they're expecting. This often settles on its own, but if she seems unwell or stays in season unusually long, a quick chat with your vet can help put your mind at ease, as occasionally a serious womb infection called pyometra can develop in unneutered females (Royal Kennel Club).
To care for her during a season, you can walk her in quieter places and at quieter times, keep her on the lead around other dogs, and give her calm, comforting attention at home. Many owners use washable dog pants to manage any mess indoors.
The teenage phase: why your dog suddenly stops listening
If your once-angelic puppy hits around eight months and seems to forget every command, you're not imagining it, and you haven't done anything wrong. Dogs go through a genuine adolescent phase, much like human teenagers.
A study led by UK researchers found that dogs were measurably harder to train and less responsive to commands around puberty, at roughly eight months, and that this dip was most noticeable with their main caregiver rather than with strangers (Asher et al., 2020). In other words, your teenage dog is most likely to ignore you, the person they're closest to. The reassuring part is that the same research found this is a passing phase: by about 12 months, most dogs' behaviour had returned to how it was before, or even improved (Asher et al., 2020).
This is one of the most important things a new owner can understand, because adolescence is sadly the age when many dogs are given up, often just before they would have grown out of it. A few things that help during these months:
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Keep training consistent and positive. Short, rewarding sessions work better than long or frustrating ones.
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Don't take the wobble personally. Lapses in recall and "selective hearing" are developmental, not defiance.
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Keep them stimulated. Sniffy walks, puzzle feeders, and gentle play soak up that teenage energy.
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Stay patient. This phase passes, and the calm adult dog is on their way.
If you're struggling, your vet or an accredited dog trainer can be a real support rather than a last resort.
Emotional maturity: when your dog finally settles
Emotional maturity is the last piece to fall into place, usually somewhere between 18 months and two years, and later for some big breeds. You'll notice your dog becoming less distractible, calmer in new situations, better at listening, and generally more settled in themselves.
You may still see flashes of the puppy they were, and that playful streak often stays for life, which is part of the joy. But the day-to-day intensity eases, and the dog you've been patiently raising starts to show up properly. Their physical needs, including how much they eat and the type of exercise that suits them, have usually shifted to those of an adult well before this point.
Should you neuter or spay, and when?
Neutering (for males) and spaying (for females) are among the most common procedures carried out on UK dogs. Neutering prevents unwanted litters and seasons, can reduce hormone-driven behaviours such as roaming, and is associated with a lower risk of certain health problems, including womb infections in females (Royal Kennel Club). For many owners, it's a sensible choice, but the question of when has become more nuanced than it used to be.
For years, the standard advice was to neuter at around six months. More recent research suggests that's too simple. A large study analysing 35 breeds found that, for several larger breeds, neutering before a dog was physically mature was associated with a higher risk of certain joint disorders and some cancers, while small breeds generally showed little of this effect (Hart et al., 2020). The researchers suggested that the best age to neuter may differ considerably depending on a dog's breed and adult size, rather than following a single rule for every dog.
So what does that mean for you? Mainly this: there's no one-size-fits-all answer, and it's a decision worth making with your vet, who can weigh up your individual dog's breed, size, sex, temperament and lifestyle. The benefits of neutering remain real for many dogs, especially around preventing unwanted litters and managing seasons, but timing can matter, particularly for larger breeds. A conversation with your vet is the best way to land on what suits your dog.
Feeding your dog from puppy to adult
Your dog's nutritional needs change as they grow, so their food should keep up. Puppies need energy and nutrients to fuel rapid growth, which is why a complete puppy recipe matters during the first year (or longer for big breeds). Keeping an eye on the everyday signs of good health helps too. For example, what their poo looks like can tell you a lot, as we cover in our guide to the puppy poop chart.
Once your dog is physically mature, they can move on to adult dog food that matches their calmer, fully grown needs and helps prevent unwanted weight gain. As with any food change, make the switch gradually over a week or so, mixing a little more of the new food in each day to give their tummy time to adjust. Large breeds often make this move later than small ones, simply because they finish growing later.
Whatever life stage your dog is at, all of our recipes are developed with veterinary and nutritionist input, and your vet is always the best person to ask about your individual dog's diet, neutering and development.
References
Asher, L., England, G. C. W., Sommerville, R., & Harvey, N. D. (2020). Teenage dogs? Evidence for adolescent-phase conflict behaviour and an association between attachment to humans and pubertal timing in the domestic dog. Biology Letters, 16(5), 20200097. https://doi.org/10.1098/rsbl.2020.0097
Hart, B. L., Hart, L. A., Thigpen, A. P., & Willits, N. H. (2020). Assisting decision-making on age of neutering for 35 breeds of dogs: Associated joint disorders, cancers, and urinary incontinence. Frontiers in Veterinary Science, 7, 388. https://doi.org/10.3389/fvets.2020.00388
Royal Kennel Club. (n.d.-a). Understanding your dog's seasons. https://www.royalkennelclub.com/health-and-dog-care/health-dog-care/health/health-and-care/a-z-of-health-and-care-issues/seasons-and-being-in-heat/
Royal Kennel Club. (n.d.-b). Neutering (castration and spaying) a dog. https://www.royalkennelclub.com/health-and-dog-care/health-dog-care/health/health-and-care/a-z-of-health-and-care-issues/neutering-a-dog-castrating-and-spaying/
