The common belief that one dog year is equivalent to seven human years is a myth. The ratio of dog years to human years actually varies depending on the dog's breed and size.
Generally speaking, the first year of a small dog's life is roughly equivalent to 15 human years, while the first year of a large dog's life is closer to 9 human years. After the first year, a small dog will age about 4 human years per year, while a large dog will age about 5-6 human years per year.
Here is a rough estimate of dog years to human years based on the dog's size:
- Small dog (under 20 pounds): Year 1 = 15 human years, Year 2 = 24 human years, Year 3 = 28 human years, Year 4 = 32 human years, and each additional year = about 4 human years.
- Medium dog (21-50 pounds): Year 1 = 12 human years, Year 2 = 24 human years, Year 3 = 28 human years, Year 4 = 32 human years, and each additional year = about 5 human years.
- Large dog (51-90 pounds): Year 1 = 9 human years, Year 2 = 18 human years, Year 3 = 27 human years, Year 4 = 36 human years, and each additional year = about 6 human years.
- Giant dog (over 90 pounds): Year 1 = 8 human years, Year 2 = 16 human years, Year 3 = 24 human years, Year 4 = 32 human years, and each additional year = about 5-6 human years.
It's important to note that these are rough estimates, and there is some variation depending on the individual dog's breed and health.