While the old saying suggests that one human year is equivalent to seven dog years, this isn’t really accurate. A dog’s age is based on its size and breed, and they also mature faster during the first few years of their lives. Therefore, calculating "dog years" isn’t a simple multiplication problem.[1][2]
How Do You Calculate Dog Years?
The outdated 7:1 ratio came about because people in the 1950s lived to be about 70 years old, and dogs lived to be about 10 years old. However, experts agree that dogs age more quickly in their early years. For example, a one-year-old dog is generally comparable to a 15-year-old person, and a two-year-old dog is comparable to a 24-year-old. After age two, the leveling off begins, and "dog years" increase annually in roughly four-year increments.[1]
Dog Years to Human Years Conversion Chart
The size of the dog is a factor as the animal ages. Here is a general guide:[1]
| Dog years | Small (20 lb or less) | Medium (21–50 lb) | Large (51–90 lb) | Huge (91 lb or more) |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 12–15 |
| 2 | 24 | 24 | 24 | 22–24 |
| 3 | 28 | 28 | 28–30 | 31–32 |
| 4 | 32 | 32–33 | 32–35 | 37–38 |
| 5 | 36 | 36–37 | 36–40 | 42–45 |
| 6 | 40 | 42 | 45 | 49 |
| 7 | 44 | 47 | 50 | 56 |
| 8 | 48 | 51 | 55 | 64 |
| 9 | 52 | 56 | 61 | 71 |
| 10 | 56 | 60 | 66 | 78–79 |
| 11 | 60 | 65 | 72 | 86 |
| 12 | 64 | 69 | 77 | 93 |
| 13 | 68 | 74 | 82 | 100–101 |
| 14 | 72 | 78 | 88 | 107–108 |
| 15 | 76 | 83 | 93 | 114–115 |
| 16 | 80 | 87 | 99–120 | 121–123 |
| 17 | 84 | 92 | — | — |
| 18 | 88 | 96 | — | — |
| 19 | 92 | 101 | — | — |
| 20 | 96 | 105 | — | — |
Using this table, seven hours in dog time depends on the dog’s size. If we assume that a dog’s day is also seven hours long, then seven "dog hours" would translate as follows:
- Small dog: 44 human years
- Medium dog: 47 human years
- Large dog: 50 human years
- Huge dog: 56 human years
Why Do Small Dogs Live Longer?
While larger size normally indicates greater longevity among most mammals, dogs tend to follow a different pattern. Small dogs usually live longer than their larger counterparts due to genetic, physiological, and evolutionary factors. Smaller dogs benefit from genetic diversity, which contributes to their longer life expectancy. Smaller dogs also tend to mature more slowly after their initial growth spurt, which contributes to their extended lifespan.[3]
People Also Ask
How long do different sizes of dogs live?
Small dogs (20 lb [9 kg] or less) typically live 10–20 years, medium dogs (21–50 lb [9.5–22.7 kg]) live 10–13 years, large dogs (51–90 lb [23.1–40.8 kg]) live 8–12 years, and huge dogs (91 lb [41.3 kg] or more) live 6–10 years.[1]
At what age is a dog considered a senior?
Small dogs (20 lb [9 kg] or less) are considered seniors at 10 years and older, medium dogs (21–50 lb [9.5–22.7 kg]) at 8 years and older, and large dogs (51 lb [23.1 kg] or more) at 5 years and older.[1]
What factors affect a dog’s lifespan?
A dog’s lifespan can be affected by its breed and size. Smaller and mixed-breed dogs tend to live longer than larger and purebred dogs.[1][2][3]
Want to discover more about dog breeds?