The old adage says that a dog ages 7 dog years for each human year of its life. So - where does this come from? Well, if a human lives about 70 years, and a dog lives about 10 years, then we say that a dog ages seven times faster than a human. But, in reality, it is a bit more complicated than that. Just as a human's life expectancy depends on many factors, so does your pet's. The table shown below (courtesy of IDEXX and Fred L. Metzger, DVM DABVP), shows your pet's age with a bit more precision.

To understand the table, let's look at a couple of examples:

Example 1: 18 Year Old Cat

Pet: Cat
Weight: 10 lbs
Age of pet: 18 years

Comparison research shows that the cat is equivalent in years to a 92 year old human.

Example 2: 10 lb, 18 Year Old Dog

Pet: Dog
Weight: 10 lbs
Age of pet: 18 years

A 10 lb dog ages about as fast as a 10 lb cat. The dog’s age is equivalent to that of a 92 year old human.

Example 3: 80 lb, 10 Year Old Dog

Pet: Dog
Weight: 80 lbs
Age of pet: 10 years

An 80 lb dog ages much quicker than the smaller dog. The 10 year old 80 lb dog is equivalent to a 66 year old human. A little less than the adage of 1 human year is 7 dog years.

Example 4: 30 lb, 3 Year Old Dog

Pet: Dog
Weight: 30 lbs
Age of Pet: 3 years

A 30 lb dog is an adult after 3 years and is considered to be equivalent to a human that is 21 years old.