The 7:1 ratio is a gross oversimplification of how dogs age. No one knows where the dog years myth came from, but experts agree that it’s simply not true.
Although no one is sure exactly where this 7:1 ratio originated from, there is evidence that monks at Westminster Abbey in the 13th century were the first to put forth a similar figure of a 9:1 ratio.
The problem with this simple ratio is that it’s not an accurate reflection of reality. As Priceonomics writes:
“If this ratio had any truth to it, humans would be capable of reproducing by age seven, and high percentages of us would live to be 150.”
Researchers have now came up with a new equation to calculate your dog’s age in human years.
The new equation is based on chemical changes to a dog’s DNA. “Mammals progress through similar physiological stages during life, from early development to puberty, aging and death,” a group of researchers wrote in a new study which has not yet been published peer-reviewed journal.
The researchers found that 8 weeks in dogs corresponded to 9 months in humans, which is when both species start growing their first tiny teeth.
Retrievers have an average life span of 12 years, which corresponds with humans, which is approximately 70 years. But for adolescent and mature dogs, the relationship was “more approximate,” the researchers wrote.
Adolescent and mature dogs began to age faster compared to adolescent and adult humans, but towards the end of their lifespan, the aging (or methylation rates) of these dogs lined up again with that of older humans.
Larger breeds tend to pass away well before smaller ones. As aging researchers calculated, a ten-year-old small dog is about 56 in equivalent human years, for example, whereas a large dog is 66 and a super-big dog is 78.
So as we can see it is a bit more complex than the simple 7:1 ration commonly used.
The equation the researchers came up with to describe this relationship is as follows: 16 x ln(dog age) +31.
In simpler terms, take the natural log of the dog’s age, multiple by 16 and then add 31.
But bear in mind, different breeds have different rates of aging. Further studies will need to be done to figure out the the equation based on the lifespan of different breeds.