Contrary to popular belief, one "dog year" does not equal seven human years. We've seen many 20-year-old dogs in our practice, but we are yet to even hear of any 140-year-old humans. Along the same line, a dog that is two years old is an adult. A 14-year-old teenager is just that... a teenager.
The most accurate way to determine the relative age of your dog is to know the life expectancy of your dog's breed. Small breeds tend to live longer, frequently 14 to 17 years or longer. Giant breeds, like Great Danes, have a life expectency that is significantly shorter. Even with that knowledge, however, there is no easy multiplier you can use to determine the relative age of your pet because of the many variables in the aging process of canines, particularly in the first few years.
While it is fun to know the relative age of your pet in human years, it can also help you understand your dog's behavior, his special needs as he gets older, and different nutritional requirements as he progresses through life.
The chart shown is a fairly accurate measure of the relative age of the average dog when compared to humans.
The good news is that pets, like people, have a longer life expectancy today than ever before; primarily due to better healthcare and nutrition.