Dog age to human years chart, by size
A small, medium or large dog is about 15 in human years at 1, 24 at 2 and 36 at 5: until then, size makes no difference. A giant breed is about 12 at 1 and already 45 at 5. After that, the bigger the dog, the faster it ages: at 10, a small dog is about 56, a medium dog 60, a large dog 66 and a giant 79.
| Dog's age | Smallunder 10 kg | Medium10 to 25 kg | Large25 to 45 kg | Giantover 45 kg |
|---|---|---|---|---|
| 1 year | 15 years | 15 years | 15 years | 12 years |
| 2 years | 24 years | 24 years | 24 years | 22 years |
| 3 years | 28 years | 28 years | 28 years | 31 years |
| 4 years | 32 years | 32 years | 32 years | 38 years |
| 5 years | 36 years | 36 years | 36 years | 45 years |
| 6 years | 40 years | 42 years | 45 years | 49 years (senior) |
| 7 years | 44 years | 47 years | 50 years (senior) | 56 years (senior) |
| 8 years | 48 years | 51 years (senior) | 55 years (senior) | 64 years (senior) |
| 9 years | 52 years | 56 years (senior) | 61 years (senior) | 71 years (senior) |
| 10 years | 56 years (senior) | 60 years (senior) | 66 years (senior) | 79 years (senior) |
| 11 years | 60 years (senior) | 65 years (senior) | 72 years (senior) | 86 years (senior) |
| 12 years | 64 years (senior) | 69 years (senior) | 77 years (senior) | 93 years (senior) |
| 13 years | 68 years (senior) | 74 years (senior) | 82 years (senior) | 100 years (senior) |
| 14 years | 72 years (senior) | 78 years (senior) | 88 years (senior) | rarely reached |
| 15 years | 76 years (senior) | 83 years (senior) | 93 years (senior) | rarely reached |
| 16 years | 80 years (senior) | 87 years (senior) | rarely reached | rarely reached |
Values from the "Comparative Age of Dogs and Humans" chart in the Dog Owner's Home Veterinary Handbook (2007). Shaded cell: senior age for that size. A dash marks an age dogs of that size rarely reach.
Puppy age in human years, month by month
The first year isn't spread evenly: a puppy grows up very fast until puberty, then more slowly. We follow the developmental stages a 2020 study (Cell Systems) lines up with a child's: at around 2 months, when its milk teeth come through, a puppy matches a baby of about 1, at around 6 months, the age of puberty, a child of about 12, and at 1 year a teenager of 15. Puberty generally comes later in a large dog than in a small one: a giant breed's curve rises more slowly, to about 10 at 6 months and 12 at 1 year, the handbook's figure for its size.
| Puppy's age | Human age |
|---|---|
| 2 months | 1 year |
| 3 months | 4 years |
| 4 months | 7 years |
| 5 months | 9 years |
| 6 months | 12 years |
| 7 months | 13 years |
| 8 months | 13 years |
| 9 months | 14 years |
| 10 months | 14 years |
| 11 months | 15 years |
How to calculate your dog's age in human years
It takes three steps, from your dog's age and adult size.
- Count 15 years for the first yearA 1-year-old small, medium or large dog is about 15 in human years, a giant breed about 12. For a puppy, count about 1 year at 2 months and 12 at 6 months, the age of puberty (10 for a giant breed).
- Add 9 years for the second yearAt 2, a small, medium or large dog is about 24 in human years. A giant breed adds 10, to about 22.
- Then add the years for its sizeFor a small dog (under 10 kg), add 4 years a year. A medium (10 to 25 kg) or large dog (25 to 45 kg) keeps that pace until 5, about 36, then adds about 4 to 5 years a year if medium and 5 to 6 if large. A giant breed (over 45 kg) adds about 7 years a year. The chart on this page gives the value for every age.
Example: an 8-year-old small dog is about 24 + 6 × 4 = 48 in human years. A medium dog the same age is about 51, from the chart.
Convert human years to dog years
The reverse calculation: at what age will your dog be 40, 60 or 80 in human years? Up to 36 human years, size makes no difference for a small, medium or large dog. Beyond that, a large dog reaches each age sooner than a small one, and a giant breed, past its first two years, sooner still.
Example for 40 human years:
- Small6 years
- Medium5 years and 8 months
- Large5 years and 5 months
- Giant4 years and 3 months
| Human age | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 12 years | 6 months | 6 months | 6 months | 1 year |
| 15 years | 1 year | 1 year | 1 year | 1 year and 4 months |
| 20 years | 1 year and 7 months | 1 year and 7 months | 1 year and 7 months | 1 year and 10 months |
| 24 years | 2 years | 2 years | 2 years | 2 years and 3 months |
| 30 years | 3 years and 6 months | 3 years and 6 months | 3 years and 6 months | 2 years and 11 months |
| 40 years | 6 years | 5 years and 8 months | 5 years and 5 months | 4 years and 3 months |
| 50 years | 8 years and 6 months | 7 years and 9 months | 7 years | 6 years and 2 months |
| 60 years | 11 years | 10 years | 8 years and 10 months | 7 years and 6 months |
| 70 years | 13 years and 6 months | 12 years and 2 months | 10 years and 8 months | 8 years and 10 months |
| 80 years | 16 years | 14 years and 5 months | 12 years and 7 months | 10 years and 2 months |
The "one pet year equals seven human years" myth
This simple rule is wrong. Dogs and cats become adults in barely one to two years, then age more slowly. One early year of life is worth far more than seven human years, while a year late in life is worth less.
Why charts disagree on the first year
Some charts give a small dog 20 human years at age 1, 18 for a medium dog and 16 for a large one, on the idea that small dogs mature faster. A 2020 DNA-based study goes as high as about 31. There is no official conversion. Our calculation follows the comparative chart of a US veterinary handbook: about 15 years for the first year and 9 more for the second for a small, medium or large dog, 12 and then 10 more for a giant breed. Size makes the difference after that, year by year.
Why big dogs age faster
Across mammal species, the biggest live the longest. Within a species, the biggest individuals often live shorter lives, and dogs are the clearest case: a giant breed lives about 4 years less than a small dog on average.
A 2013 study in The American Naturalist, covering 74 breeds, shows that large dogs don't start ageing earlier: they age faster. Its authors conclude that large dogs die young mainly because they age quickly. Their very fast growth as puppies is one of the leads put forward, with no definitive explanation so far.
That's why, at 10, a small dog is about 56 in human years and a giant breed about 79.
Dog life expectancy by size
A 2023 study based on the records of several million dogs seen at US veterinary clinics gives the life expectancy at birth for each size group. Across all dogs, it is 12.7 years.
That figure includes dogs that die young: once past its first years, a dog's total life expectancy is longer.
| Size | Adult weight | Life expectancy |
|---|---|---|
| Toy | under 5.5 kg | 13.4 years |
| Small | 5.5 to 11 kg | 13.5 years |
| Medium | 11 to 26 kg | 12.7 years |
| Large | 26 to 45 kg | 11.5 years |
| Giant | 45 kg and over | 9.5 years |
The main life stages
Understanding your pet's life stage helps you adapt its diet, activity and health care.
Puppy
Fast growth: vaccines, deworming, socialisation and identification (microchip) are the priorities of the first months.
Adult
Prime years: one vet visit a year, a suitable diet and regular activity are enough to keep them healthy.
Senior
Watch weight, teeth and joints. Two vet visits a year help catch health issues early.
An estimate, not a diagnosis
This calculator gives a ballpark figure. Every animal ages at its own pace, and only a vet can properly assess its health.
Our sources
- Method (dog), from age 1: the values of the "Comparative Age of Dogs and Humans" chart in the Dog Owner's Home Veterinary Handbook (Eldredge et al., 4th edition, 2007), from 1 to 16, taken as printed, with interpolation between birthdays. Its sizes, given in pounds, match ours: small up to 20 lb (9 kg), medium 21 to 50 lb (9.5 to 23 kg), large 51 to 100 lb (23 to 45 kg), giant over 100 lb (45 kg).
- Dog and cat life expectancy: Montoya et al., "Life expectancy tables for dogs and cats derived from clinical data", Frontiers in Veterinary Science, 2023 (US veterinary clinic records, figures checked on 31 October 2026). doi.org
- Why large dogs age faster: Kraus, Pavard and Promislow, "The size-life span trade-off decomposed: why large dogs die young", The American Naturalist, 2013 (74 breeds). doi.org
- Dog life stages: the AAHA canine life stage guidelines, 2019 (the senior stage starts at the last quarter of life expectancy, and the first heat comes anywhere from 4 months in some small breeds to 24 months in some large ones). doi.org
- Puppy age before 1 year and the DNA method (dog): Wang et al., "Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome", Cell Systems, 2020 (dog developmental stages lined up with human ones, 2 months ≈ 1 year and 6 months, puberty, ≈ 12, and the formula 16 × ln(age) + 31, derived from Labradors). doi.org
Going further
Welcoming an animal well also means planning ahead and being ready to react.
FAQ - Frequently asked questions
How old is a 1-year-old dog in human years?
About 15 for a small, medium or large dog, and about 12 for a giant breed. In one year a puppy becomes a young adult, which is why the simple times-seven rule badly underestimates the early years.
How old is a 2-year-old dog in human years?
About 24 for a small, medium or large dog, and about 22 for a giant breed. Those three sizes then keep the same pace until 5, about 36 in human years, and size makes the difference after that. A giant breed ages faster from its third year.
How old is a 10-year-old dog in human years?
It depends on size: about 56 for a small dog, 60 for a medium dog, 66 for a large dog and 79 for a giant breed. The chart on this page gives the year-by-year equivalent for every size.
How old is a 15-year-old dog in human years?
About 76 for a small dog, 83 for a medium dog and 93 for a large dog. Large and giant breeds rarely reach that age: their average life expectancy is 11.5 and 9.5 years.
How old is a 6-month-old puppy in human years?
About 12. A puppy grows up very fast until puberty, which often comes at around 6 months, like a child of about 12. At around 2 months, when its milk teeth come through, it matches a baby of about 1, and a 3-month-old puppy is about 4. Puberty generally comes later in a large dog than in a small one: for a giant breed, we count about 10 at 6 months and 12 at 1 year.
At what age is a dog considered old?
It depends on size: around 10 for a small dog, 8 for a medium dog, 7 for a large dog and as early as 6 for a giant breed. The AAHA guidelines (2019) start the senior stage at the last quarter of life expectancy, which depends on breed and size. From then on, more regular vet check-ups are recommended.
How long do dogs live?
12.7 years on average at birth, according to a 2023 study of several million dogs seen at US veterinary clinics. A small dog lives 13.5 years on average, a medium dog 12.7, a large dog 11.5 and a giant breed 9.5.
Why does my dog's size change the result?
The bigger the dog, the faster it ages. A study of 74 breeds (The American Naturalist, 2013) shows that large dogs don't start ageing earlier: they age faster. A giant breed lives 9.5 years on average, against 13.5 for a small dog. That's why we ask for size.
Why do some charts say a 1-year-old dog is 20?
There is no official conversion. Some charts give a small dog 20 human years at age 1, on the idea that it matures faster than a large dog. Our calculation follows the comparative chart of a US veterinary handbook, which counts about 15 years for the first year for a small, medium or large dog, and 12 for a giant breed. For cats, the AAFP-AAHA feline guidelines also count 15.
How do I convert human years to dog years?
Read the chart on this page backwards. For a small, medium or large dog, size doesn't matter up to 36 human years: 15 human years is age 1, 24 is age 2 and 36 is age 5. Beyond that, the bigger the dog, the sooner it reaches each age: 60 human years is about 11 for a small dog, 10 for a medium dog and 9 for a large dog. A giant breed is already 45 in human years at 5. The converter on this page works it out for every size.
Does this replace the vet?
No. It's an estimate to help you understand your dog's life stage. Only a vet can properly assess its health and true age.