By the Numbers: How Old is Your Dog in Human Years?

Today, there are a number of updated methods and formulas for estimating canine age. photo: AdobeStock

Just this past month, Bobi, the world’s oldest dog according to Guinness World Records, celebrated his 31st birthday in the Portuguese village of Conquieros. The oldest verified human on the planet lived to be 122 ½. But if we use the classic formula of one dog year for every seven human years, Bobi would be an astounding 217 human years old.  

How did this traditional - yet clearly inexact - formula come about?  Turns out no one is quite sure. 

The popular 7:1 formula has been around since at least the 1950s, but despite its longevity, it is not supported by science or experience. One possible explanation is that it was based on older statistics showing that people had an average life expectancy of about 70 years compared to a dog’s average of 10 (these figures have been revised upwards over the last three-quarters of a century largely due to better health care for dogs and humans). The formula may have been an attempt to educate dog owners on how fast a dog ages compared to humans. Or it could have been a way to encourage dog guardians to bring their furry friends in for a vet exam at least once a year.

Our beloved canines age so much faster than humans and we who love them are acutely aware of this. But the aging process may vary wildly due to a dog’s size, genetic breed mix, diet, and other factors. Small breed dogs typically reach maturity faster and age more slowly than larger breed dogs. A Chihuahua might achieve adulthood before one year of age and live to be 20, while a Great Dane might still be growing after two years of age and only live to be eight or nine years old. 

Today, there are a number of updated methods and formulas for estimating canine age. The American Veterinary Medical Association now holds that the first year of a medium-sized dog’s life is equivalent to 15 human years. In other words, the first year for dogs is a quick sprint to becoming a teenager.  A dog’s second year equals about 9 human years, with each succeeding year equalling roughly 4-5 human years. 

Some newer formulas also consider the size of the dog. As noted above, large dogs age more quickly than smaller dog breeds. Small dogs are considered senior at 7-8 years, but we all know they have plenty of life left in them at that age. Large breed dogs tend to have shorter lifespans and are often considered senior at 4 to 5 years of age.   

Still not sure where your pup falls on the age spectrum? Here’s a handy chart from the American Kennel Club that shows a dog’s likely age in human years by size. 

Or you may prefer this chart from the University of California Davis showing dog/human age equivalencies.  

In an ongoing quest for more precise measurements, scientists are now studying the methylation patterns of the DNA in aging dogs and humans. Methylation is a biologic process in which methyl groups are added to DNA molecules creating a “molecular clock” to measure age. Stay tuned, as this method evolves to help us age our pooches more exactly. At least one age test kit for dogs using DNA technology is already available online. 

Meanwhile, we can all continue to observe our own dogs for signs of aging. Their eyes may become cloudy, and their hair may turn gray, especially around their muzzle and eyes. Sometimes their hair coat may start to thin out as it often does in older humans. Accumulation of dental calculus and tartar, tooth wear and loss, and periodontal disease generally increase with age. Our dogs might become hard of hearing. Even their body shape may change with accumulation of fat pads over their lower back or muscle wasting along the back and hind legs. Most likely, we will notice our dogs are slowing down. 

Modern veterinary medicine has helped extend our dogs' lives. In my own practice, I see dogs that are approaching 20 more regularly these days. I also have the privilege of meeting many old and fragile dogs at their end of life. I find that, as with humans, our aging canines become beautiful in their own ways. Sometimes they still have puppy characteristics, while others look like ancient beings. Despite graying muzzles, cloudy eyes, or hair loss, these beloved friends are nurtured and loved by their humans until the very end. Our canine companions teach us much about the aging process and about our own mortality.  

But no matter how old your dog is, remember to love and cherish them. A dog of any age will bring unconditional love and companionship, and their eyes, no matter how cloudy, will still reveal their strong spirit.  

Bobi, the 31-year-old canine, teaches us that canine aging is a gamut of possibility and hope. All the rest is just numbers.