If you've always thought of your dog's age in terms of each year equaling about 7 in human years, you're not completely off base. If you have a 3-year-old pooch, he is around 21 years in human equivalency (7x3=21). However, for a more accurate gauge of how old your dog really is, it can get more complicated.
Researchers at the University of California San Diego School of Medicine studied doggie DNA and compared it how human DNA ages. They came up with a complex formula multiplying the logarithm they created by 16 and adding 31 (human_age = 16ln(dog_age) + 31). But hey, we're not trying to revisit Algebra II here.
Instead, Dr. Sara Ochoa, a Texas veterinarian and consultant for doglab.com, says, "The one year for every seven years is pretty accurate to follow." If you want to get fancier, there's a formula we'll call "15, 9, 5" that you can use. In this one your dog ages as follows:
Year one is equivalent to 15 human years
Year two is equivalent to nine human years
Each year thereafter is equivalent to four to five human years
With this formula, the same three-year-old dog in the above example would be about 28 rather than 21. This formula considers a dog's breed and size, aspects that influence how he ages. "Small dogs tend to follow the one year to five-year rule, where larger breed dogs who don't live as long follow the one year to 10-year rule," says Dr. Ochoa.
Why Dogs Age Differently
Researchers think small, medium, and large breed dogs tend to age about the same until they're around six. Then larger dogs start aging faster. This might be due to how fast larger dogs grow compared to smaller dogs, exposing them to more abnormal cell growth or cancerous cells. It may also be because they contract age-related diseases sooner than smaller dogs.
In any case, both formulas are still best guesses when it comes to comparing your dog's age to human years. It's a gauge that helps you and your vet look for age-related changes and make health and wellness decisions that benefit your pup based on how old he is and what veterinarians know about senior dog care.
How to Keep Your Dog Young
"I think that these rules are good to follow to understand how your dog should be acting," says Dr. Ochoa. "Understanding that your dog is similar to an 80-year-old will help you understand why they are slowing down and not moving as much," she says. It also helps explain when dogs have issues like poorer eyesight, trouble hearing, joint pain, and less pep in their step.
It helps us understand why younger dogs who are like a 15 or 25-years-old have better health, higher activity levels, less disease, the energy of a teenager or young person.
Plus, as a dog owner, you can be on the lookout for signs of aging in your dog as he rounds six years if he's a medium to large dog or eight years old for small dogs. You're the best observer of things like activity levels, eating habits, weight gain, and behaviors that may indicate age-related changes in your dog like not jumping, bumping into things, or having trouble getting up and down.
Meanwhile, remember that your dog's real age is based on way more complicated factors than these formulas can offer including their breed, their size, their genetics as well as their overall health, and factors like activity and nutrition.
Talk to your vet to learn more about how to use your dog's age to his benefit to keep him happy and healthy for as long as possible.