If your dog is five years old, that means he is the same physiologic age as a 35-year-old person, right? Well, actually not. The theory that every year in a dog's life is the same as seven years in ours is commonly known but unfortunately not very accurate.

For example, a one-year-old beagle has passed puberty. A seven-year-old child likely has not. A seven-year-old Mastiff is considered geriatric, but a 49-year-old person is not.

For a more accurate comparison between physiologic age of dogs, follow this formula:

A one-year-old small or medium sized dog is about 15 human years old. When the dog reaches two, he is the equivalent of a 24-year-old person. After that, each year is about four human years. This means that a nine-year-old dog is about the same as a 52-year-old person.

Large and giant breed dogs initially age slower but then age quickly. At one year of age, he is about the same physiologically as a 12-year-old child. After that, each year follows the standard seven human years.

The average canine life span is around 12 years but differs from breed to breed. By the time most dogs reach seven years of age, they are entering their senior years. For giant breed dogs, five years old is considered the beginning of old age. The record for the longest canine life span is 29 years.