Myth: One dog year equals about seven human years.

There is a popular belief that dogs age seven years for each calendar year because the lifespan of a dog is about one seventh in duration to a human’s average lifespan. So a two year old dog corresponds to a fourteen year old human teenager in the terms of this aging processes.

This model, however, is completley incorrect. In fact, determining the exact age of a particular dog, relative to a human scale, is much more complex than that with the ratio of dog years to human years varying with the weight, breed, and health condition of the dog.

Canine aging is much more rapid during the first two years of a dog’s life relative to the first fourteen years of a human’s life. It turns out, for many breeds, the first year of a dog’s life is equal to about 14-15 human years. Later, depending on the dog`s size in pounds typical for its breed, the same number of actual years corresponds to different number of human years, with this scale varying greatly from breed to breed.

There are four main groups of dogs each having a different ratio of translating dog years to human years: small dogs (20 pounds or less), medium dogs (21-50 pounds), large dogs (51-90 pounds) and giant breeds (more than 90 pounds). Large dogs mature more slowly but at the age of five they will be considered elderly, while small and toy breeds are not considered seniors until the age of ten.

So overall, after the first two years, the ratio is about 5 dog years to 1 calendar year for small and medium breeds and 6-7 dog years to 1 calendar year for large and giant breeds. That is why at 10 years of age a Great Dane would be considered 80 years old on the human age scale while a Pug would only be 64.

So the bottom line is, the old thumb rule that one dog year equals seven years of a human life is not at all accurate. The ratio is higher during first years of the dog’s life and decreases as the dog ages.

Bonus Facts:

There is a somewhat simplified generic formula used by many canine experts for determining dog age: 10.5 dog years per human year for the first 2 years, then 4 dog years per human year for each year after.

There are ways to estimate a dog’s age when his birth date is unknown. First of all, a dog’s age is apparent from the degree of growth and the condition of their teeth. Overall, the vet will estimate the dog’s age based on a physical exam of bones, joints, muscles and internal organs.

Mixed breeds tend to live longer due to greater genetic diversity while some pure breeds are prone to diseases.

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