Why? Many Questions Answered

The age-old adage that one dog year equals seven human years derives from the simple mathematical division of the average human lifespan by the average canine lifespan.

It’s true that dogs do age much faster than humans because of their higher metabolic rate; generally speaking, the larger the mammal, the slower the metabolism and the longer the life However, it’s now generally accepted that the seven-to-one rule of thumb for a dog’s “realistic” age is inaccurate; for instance, it’s not uncommon for dogs to live to the age of fifteen, but few humans live to 105

It’s believed that the seven-year rule should not be applied proportionally, and that, while it might be appropriate for the middle section of a dog’s life, the beginning or final developmental phases cannot be correlated to those of
a human A dog tends to be fully sized and sexually mature at the age of one, but the same cannot be said of a human of seven A more accurate method of calculating a dog’s “realistic” age is to allocate twenty-one years for the first year.

(i e , when dog and human both reach adulthood) and then
four years for every additional year

The size and breed of a dog are also factors that impact on how fast it ages Larger dogs age the fastest, so even the above rule cannot be applied to all breeds of dogs In fact, the older the dog, the more accurate the seven-to-one ratio becomes Roughly, a large ten-year-old dog is considered to be seventy-eight, whereas a small ten-year-old dog would be fifty-six