Medium dogs sit in the middle of the ageing scale — and the middle is where most dogs are. A medium dog weighs 10 to 25 kg, ages a little faster than a small dog and a little slower than a large dog, and typically lives 10 to 14 years. This guide is the medium dog age calculator in words: the chart for medium dogs from 1 to 15 years, the formula behind it, when a medium dog counts as a senior, and how medium-dog ageing compares with small, large, and giant dogs. It covers medium breeds such as French Bulldogs, Bulldogs, Beagles, Pembroke Welsh Corgis, Australian Shepherds, Siberian Huskies, Shetland Sheepdogs, Brittanys, Cocker Spaniels, Border Collies, Chow Chows, Australian Cattle Dogs, Basset Hounds, and Dalmatians — and it uses the AVMA/AKC size model, the same model vets use.
The old rule of multiplying by seven is wrong for every dog. A 1-year-old medium dog is already about 15 in human years, not 7, and a 10-year-old medium dog is about 64, not 70. The seven-times rule overstates a medium dog's age in later life and understates it in the first year, which is exactly when owners most need accurate guidance about training, feeding, and vet care. Use the chart below instead — or the dog age calculator, which applies the same model to any size.
How the medium dog age formula works
The AVMA/AKC size model works in three steps. The first year of a dog's life equals about 15 human years. The second year brings the total to about 24 human years. After that, you add about 5 human years per dog year for a medium dog — compared with 4 for a small or toy dog, 6 for a large dog, and 7 for a giant dog. The formula for a medium dog aged two years or more is therefore human years ≈ 24 + (dog age − 2) × 5.
For example, a 5-year-old medium dog is about 24 + 3 × 5 = 39 in human years. A 10-year-old is about 24 + 8 × 5 = 64. A 15-year-old is about 89. These are estimates, not exact conversions: individual dogs vary with genetics, diet, health, and care, and the model is a population average. What matters is the stage of life the number points to — puppy, adult, or senior — because the stage, not the number, is what should change food, exercise, and vet visits.
A second estimate comes from the UCSD epigenetic study (Wang et al., Cell Systems 2020), which gives human age = 16 × ln(dog age) + 31. For a 5-year-old medium dog that gives about 57, against 39 from the size model — the two models disagree because they measure different things, and the size model is the one vets use for life-stage decisions. Treat the UCSD figure as a research curiosity, not a clinical tool. The senior dog age calculator applies the size model to your dog's size and tells you when the senior stage begins.
Medium dog age in human years chart
Use this chart for medium breeds of 10 to 25 kg. Find your dog's age in the left column and read across. The middle column is the AVMA/AKC size model; the right column is the UCSD formula as a second opinion.
| Dog age (years) | Human years (AVMA/AKC size model) | Human years (UCSD formula) |
|---|---|---|
| 1 | 15 | 31 |
| 2 | 24 | 42 |
| 3 | 29 | 49 |
| 4 | 34 | 53 |
| 5 | 39 | 57 |
| 6 | 44 | 60 |
| 7 | 49 | 62 |
| 8 | 54 | 64 |
| 9 | 59 | 66 |
| 10 | 64 | 68 |
| 11 | 69 | 69 |
| 12 | 74 | 71 |
| 13 | 79 | 72 |
| 14 | 84 | 73 |
| 15 | 89 | 74 |
The chart shows a medium dog's steady middle course. At 7 years old a medium dog is roughly 49 in human years — a person in their late forties, still active but no longer young. At 10 the equivalent is 64, and at 12 it is 74. Compare that with a small dog, where 10 years is about 56, and a giant breed, where 10 years is about 80: the same birthday means a different stage of life depending on size. A Beagle that lives 12 to 15 years, or a Border Collie that lives 12 to 15 years, spends most of its life as an adult — but the senior stage arrives earlier than it does for a small dog, so the shift to senior care should not be left late.
When is a medium dog a senior?
Medium dogs usually become seniors earlier than small dogs: as a rough guide, from about 8 to 10 years old, which is the last quarter of a typical medium-dog lifespan of 10 to 14 years. Before that age, a medium dog is an adult, even if it is grey around the muzzle or a little slower on walks. From about 8, twice-yearly vet checks, a diet review, and attention to teeth and joints are sensible — medium breeds include many active working and herding dogs, and joint wear is the change owners most often notice first.
The signs of ageing in a medium dog are the familiar ones: sleeping more, hesitating before jumping into the car or onto furniture, stiffness after rest, cloudy eyes, and a change in appetite or weight. Weigh a medium dog monthly — a 1 kg change is a real change on a 15 kg dog — and mention any change to your vet promptly. An older medium dog may need a ramp for the car, a warm bed, and shorter but still regular walks, and it may need its food adjusted: most senior medium dogs need fewer calories, because they move less, but they still need good protein to hold muscle.
Medium dogs vs small and large dogs: ageing compared
The most consistent finding in dog-ageing research is that big dogs age faster than small dogs. A toy breed may live 12 to 16 years, a small breed 12 to 15, a medium breed 10 to 14, a large breed 10 to 12, and a giant breed only 7 to 10. Scientists still debate exactly why — faster growth, more cell divisions, and a higher lifetime load on the heart and joints are all part of the explanation — but the practical effect is clear: a medium dog has fewer years than a small dog and more than a large dog, and its senior years arrive in between.
That middle position is worth remembering when you compare your dog with others. A 9-year-old medium dog is a senior; a 9-year-old small dog is still an adult. The same age means different care, different food, and different expectations — and comparing your medium dog with a neighbour's small dog of the same age will mislead you in both directions. The dog age in human years chart puts every size on one page so you can compare directly, and the small dog age guide shows how the other end of the scale works.
What affects how fast a medium dog ages
Genetics sets the range, but daily life moves a dog within it. Weight is the factor with the clearest evidence: dogs kept lean tend to live longer and stay mobile longer than overweight dogs of the same breed, and the effect is easy to see in a medium dog, where a few extra kilograms load joints that are already working hard in an active breed. Diet quality matters less as a single magic ingredient and more as consistency — a complete, balanced food suited to the dog's life stage, fed in measured amounts rather than free-fed, with treats kept to a small share of daily calories. Exercise should be daily and suited to the dog: many medium breeds were developed to work all day, and a medium dog that never gets to run, sniff, and think loses muscle and confidence.
Veterinary care is the other big lever. Annual checks catch dental disease, lumps, heart murmurs, and weight drift early, when they are cheapest and easiest to manage. For medium breeds, joint care deserves special attention: watch for stiffness after rest, hesitation on stairs, or reluctance to jump, and mention it to your vet rather than assuming it is just old age. The Beagle age guide and the Border Collie age guide show how the same chart applies to two of the best-known medium breeds.
For related reading, see the dog age calculator, the dog age in human years chart, the dog breeds hub, the Beagle age guide, the Border Collie age guide, the small dog age guide.
Frequently asked questions
How old is a 5-year-old medium dog in human years?
About 39 human years on the AVMA/AKC size model (24 + 3 × 5). A 5-year-old medium dog is a mature adult — roughly equivalent to a person in their late thirties.
How old is a 10-year-old medium dog in human years?
About 64 human years (24 + 8 × 5). A 10-year-old medium dog is a senior, roughly equivalent to a person in their mid-sixties, and twice-yearly vet checks are sensible from about this age.
When is a medium dog considered a senior?
As a rough guide, from about 8 to 10 years old, the last quarter of a typical medium-dog lifespan of 10 to 14 years. Your vet may move the boundary earlier or later depending on your individual dog's health.
Do medium dogs live longer than large dogs?
Yes. Medium breeds typically live 10 to 14 years, against 10 to 12 for large breeds and 7 to 10 for giant breeds. The difference is real but smaller than the gap between small and giant dogs.
Is the 'multiply by 7' rule right for a medium dog?
No. It gives 35 human years for a 5-year-old medium dog, against about 39 on the size model, and 70 for a 10-year-old, against about 64 — and 7 for a 1-year-old, against about 15. Use the chart above or the dog age calculator instead.
How long do medium dogs live?
Typically 10 to 14 years. Weight, diet, exercise, and veterinary care all move an individual dog within that range or beyond it — a Beagle typically lives 12 to 15 years and a Border Collie 12 to 15 years.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.