Fact vs. Fiction: How to Calculate Dog Years

Dogs are those mainstay companions by which we track our years, which is maybe why we want to know how to track their years. We do so not only out of love for our canine friends, but also because knowing the stages of their lives help us, as good owners, to provide them the proper care and nutrition for their age. But if you’ve been living by the old adage that 1 human year equals 7 dog years, you may want to rethink your calculations.

Contemplating the age of our pets and comparing their lifespans to ours is not solely a pursuit of the modern era. As early as the 13th century, monks at Westminster Abbey in London inscribed on the floor, “If the reader wisely considers all that is laid down, he will find here the end of the primum mobile; a hedge lives for three years, add dogs and horses and men, stags and ravens, eagles, enormous whales, the world: each one following triples the years of the one before.” By their calculations, a human year would equal 9 dog years.


So where does the 1 to 7 calculation come from? Is it a scientific hypothesis of a more modern age? The answer is that no one really knows. It could be, as Kansas State University Veterinarian says, it was “a way to educate the public on how fast a dog ages compared to a human, predominantly from a health standpoint. It was a way to encourage owners to bring in their pets at least once a year.” In other words, a veterinarian marketing ploy. Or maybe it was simply based on the rough estimate that people lived 70 years and dogs about 10.


What we do know is that the estimate of 1 human year for 7 dog years isn’t accurate and isn’t based on science. However, we have learned a lot more about the science of canine aging in the last decade. First, the early years of a dog’s life are much accelerated compared to humans. For a medium-sized dog (and we’ll talk more about size shortly), its first year equals about 15 human years. Its second year equals about 9 years. Your two-year-old “puppy” then is actually a young 24-year-old urban professional in the dog world. After that, most dogs age between 4 and 5 human years per actual year.


If you’re looking for a more accurate calculation of your pup’s age, you can turn to a 2019 study conducted by the University of California San Diego. Scientists involved in the study concluded that a dog’s age in human years could be calculated by multiplying “the natural logarithm of the dog’s age by 16 and adding 31.” Say what? Okay, here’s some help from a natural logarithm calculator.


But even this study doesn’t consider all variables. First, only one breed was used in the study, and not all breeds are created equal as far as longevity is concerned. Web MD reports that among the longest living breeds are Maltese, Toy Poodles, Chihuahuas, Dachshunds, and Yorkies. You’ll notice that these are all small breeds (I did say we would return to size). Oddly, compared to the rest of the animal world where larger size equates to longer life, dogs are not that lucky. A study from the University of Gottingen reveals that every 4.4 pounds of a dog’s weight reduces its life expectancy by a month. To put this in perspective, if you look at the human age of 10-year-old dogs by weight, the smallest dogs (those under 20 pounds) are about 23 years younger than the largest dogs (over 100 pounds). In other words, your spry beagle may just be dealing with its mid-life crisis at 56, while your St. Bernard is one year shy of being an octogenarian at 79.


We can’t all be as lucky as the owners of Bluey, the Australian Cattle Dog that set the longevity record at 29 years old. But we can arm ourselves with more accurate information so that we know the proper nutrition, the exercise and care that is appropriate to the age of our dogs.


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Ivan Young is a writer from Happy Writers, Co. in partnership with Werever, the outdoor kitchen cabinet designer

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