Most people think that calculating the age of dogs and cats in “human years” is quite simple: multiply their age by seven. For example, a 4-year-old dog or cat would actually be 28 years old in human years.

But when you really begin weighing out the arithmetic, this method doesn’t add up. Say a 1-year-old dog is the equivalent of a 7-year-old human -- ** get out of here!** How many 7-year-old humans are sexually active and capable of reproducing? Dogs and cats are much more likely to have babies at 1 year old or even at 10 years old, than any person who is 7 or 70.

### Dogs

Aging is much faster during a dog’s first two years but varies among breeds. Large breeds, while they mature quicker, tend to live shorter lives. By the time they reach 5 they are considered “senior” dogs. Medium-sized breeds take around seven years to reach the senior stage, while small and toy breeds do not become seniors until around 10.

Many veterinarians agree that a pretty good guess on the age of pets can be made using the following formula. Although still simple, it is much more accurate than the seven-year method.

Assume that a 1-year-old dog is equal to a 12-year-old human and a 2-year-old dog is equal to a 24-year old human. Then add four years for every year after that. (Example: A 4-year-old dog would be 32 in human years.)

Since this method takes into consideration the maturity rate at the beginning of a dog’s life and also the slowing of the aging process in his later years, Martha Smith, director of veterinary services at Boston’s Animal Rescue League, feels that this is the more accurate calculation formula. Here is a chart, for easy reference:

A dog’s average lifespan is around 12 or 13 years, but again, this varies widely by breed. The larger your dog is, the less time it will live. Female dogs tend to live a little longer.

### Cats

Now let’s take a glimpse at a simple formula for calculating feline age in human years.

Assume that a 1-year-old cat is equal to a 15-year-old human and a 2-year-old cat is equal to a 24-year-old human. Then add four years for every year after that. (Example: A 4-year-old cat would be 32 in human years.)

The following chart shows this formula of calculation:

Cats generally live 12 to 15 years, although outdoor cats live an average of only 10 years or so.

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