How old your dog is in human years depends on their age and their size. Bigger dogs age faster, so the same birthday means something different for a Jack Russell and a Great Dane.
| Dog age | Small up to 9kg | Medium 9 to 23kg | Large 23 to 41kg | Giant over 41kg |
|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 |
| 2 years | 24 | 24 | 24 | 24 |
| 3 years | 28 | 28 | 30 | 32 |
| 4 years | 32 | 33 | 35 | 37 |
| 5 years | 36 | 37 | 40 | 42 |
| 6 years | 40 | 42 | 45 | 49 |
| 7 years | 44 | 47 | 50 | 56 |
| 8 years | 48 | 51 | 55 | 64 |
| 9 years | 52 | 56 | 61 | 71 |
| 10 years | 56 | 60 | 66 | 78 |
| 11 years | 60 | 65 | 72 | 86 |
| 12 years | 64 | 69 | 77 | 93 |
| 13 years | 68 | 74 | 82 | 101 |
| 14 years | 72 | 78 | 88 | 108 |
| 15 years | 76 | 83 | 93 | 115 |
| 16 years | 80 | 87 | 99 | 123 |
| 17 years | 84 | 92 | 104 | – |
| 18 years | 88 | 96 | 109 | – |
| 19 years | 92 | 101 | 115 | – |
| 20 years | 96 | 105 | 120 | – |
For a cross-breed, go by the weight your dog is, or will be, as an adult.
Dogs grow up much faster than people at the start. By their first birthday they're roughly as mature as a 15-year-old, and by two they're like someone in their mid-twenties. After that, each year adds about four human years for a small dog and up to seven or eight for a giant breed. Multiplying by seven makes puppies seem too young and older small dogs seem too old.
Size really does make a difference to how long dogs live. In a 2024 study led by Dogs Trust, published in Scientific Reports, which looked at more than half a million UK dogs, small purebred dogs had a median lifespan of 12.7 years, compared with 11.9 for large breeds. The study also found that flat-faced breeds tended to live shorter lives, and that females lived slightly longer than males on average.
About 15, whatever their size. A one-year-old dog is roughly as mature as a teenager, which explains a lot about adolescent dogs.
About 24, for every size. From here on, bigger dogs start to age faster.
About 36 for a small dog, 37 for a medium dog, 40 for a large dog and 42 for a giant breed. A medium-sized 5-year-old is roughly like someone in their thirties.
About 44 for a small dog, 47 for a medium dog, 50 for a large dog and 56 for a giant breed. A medium-sized 7-year-old is roughly like someone in their forties. Giant breeds are usually seniors by now, while small dogs are still middle-aged.
About 56 for a small dog, 60 for a medium dog, 66 for a large dog and 78 for a giant breed. A medium-sized 10-year-old is roughly like someone in their sixties.
About 68 for a small dog, 74 for a medium dog, 82 for a large dog and 101 for a giant breed. A medium-sized 13-year-old is roughly like someone in their seventies. Thirteen is beyond the median lifespan of most breeds.
About 76 for a small dog, 83 for a medium dog, 93 for a large dog and 115 for a giant breed. A medium-sized 15-year-old is roughly like someone in their eighties.
Age chart attributed to the American Animal Hospital Association. Lifespan findings: McMillan et al. (2024), Scientific Reports.