If you ask someone how many “human years” are in a “dog year,” the most common answer will probably be seven. It’s not clear how we got stuck on that ratio, or if multiplying a dog’s age by seven actually gives us a truer sense of how old that dog is in the context of our lifespans, but scientists have determined that this method of age calculation isn’t really accurate.
Dog Years to Human Years: Early Research
In the 1950s, French researcher A. Lebeau recognized that converting human years to dog years wasn’t so simple. While dogs do mature and age faster than people do, the relationship between our ages and their ages isn’t constant over time, so just multiplying by seven doesn’t always work.
By looking at dogs’ and humans’ maximum life spans and “life-stage markers,” like puberty, adulthood and old age, Lebeau worked out a system that scientists and veterinarians think is more accurate for determining dog years.
According to Dr. Kathryn McGonigle, clinical associate professor of internal medicine at the University of Pennsylvania School of Veterinary Medicine, dogs generally reach adulthood within the first two years of their lives and every year after that is equivalent to approximately four human years, not seven.
“Aging is very different across species, and it is absolutely true that dogs and cats age faster [than humans do],” she says. “You may have a pet that goes through his infancy, his preteens and his teens and gets into adulthood by age two.” She calls these first two dog years “the first 15 to 24” human years.
Discovering a Dog Year Calculator
In 1997, a team of veterinarians led by Gary Patronek set out to find an improved method for converting dog years to human years or, as they put it, “chronological ages” to “physiological ages.”
One issue they found with Lebeau’s work was that it didn’t account for breed, body size and weight, which can influence a dog’s lifespan and the rate at which it ages. Large breeds, like Great Danes, tend to age faster relative to small breeds, like Chihuahuas.
Patronek’s team collected data on more than 23,000 pet dogs from veterinary databases to determine the average life span for different sized breeds. Using that, they came up with a formula for converting dog years to human years that’s a bit more complicated than multiplying by seven (and not easy to do off the top of your head).
Below are the calculations the scientists found when they applied the formula to dogs in different weight groups. As you can see, size does matter, and two dogs that are the same age can have very different ages in human years if they’re different sizes:
Why Are Dog Years Important?
Why is knowing your dog’s age in human years important? Well, you wouldn’t treat a teenager the same way as a senior citizen, so calculating your dog’s physiological age as accurately as possible can help you and your veterinarian give them the best care, food and exercise that’s appropriate for their age.
In addition to a dog’s breed and size, environment and diet will impact their aging process, and McGonigle recommends feeding a high-quality diet, maintaining a lean body mass, and providing plenty of exercise and mental stimulation as ways to keep your pet healthy throughout his or her life, particularly into their senior years.
Though there aren’t as many studies on aging in pets as there are on aging in people, McGonigle says that dogs do experience aging changes similarly to humans, including changes to their hearing, vision, mobility and disease processes. Working with your veterinarian throughout your pet’s life, particularly as they age, can help improve your pet’s senior years.
“Pets have an incredible ability to hide their underlying disease processes,” she says. “We rely heavily on the physical exam and labwork findings to let us know if something’s not quite right.”
Once your pet has reached the age of seven, consider twice yearly exams and bloodwork to help diagnose and treat conditions related to age, including cancer, chronic kidney disease and endocrine or hormonal diseases like diabetes, she says.
Chart: via National Library of Medicine National Institutes of Health