If there is one myth that many of us take for truth, it is this: multiply the dog age by seven to calculate how old your faithful four-legged friend is in human years. So if you had a four-year-old dog, he’d be the same age as a 28-year-old man. Researchers are now however wiping this myth off the table. Instead, they present a new, scientific method that allows you to really find out what your dog’s age is in human years.

The researchers studied blood samples from 105 different labradors. And from this, an interesting, but perhaps not such surprising, finding rolled out. The researchers found that when dogs are still young, they age faster compared to humans. For example, a one-year-old dog is similar to a 30-year-old person. And a four-year-old dog looks like a 52-year-old. Around the seventh year of a dog’s life, the aging process begins to slow down. Dogs and humans do not age at the same rate during their lives. There is no perfect linear comparison, as the rule of thumb of 1:7 suggests. “This makes sense when you think about it,” says researcher Trey Ideker. “After all, a nine-month-old dog can already have puppies. That’s why we knew that the 1:7 ratio is not an accurate measure.”

The researchers decided to develop a new, scientific method that accurately reflects the comparative age of your four-legged friend. The new formula is based on the altered patterns of so-called methyl groups in the genomes of dogs and humans as they age. This means that the new formula provides a method to determine the age of a cell, tissue or organism based on the reading of the chemical modifications such as methylation. This affects which genes are ‘on’ or ‘off’ without changing the hereditary genetic sequence itself. “These epigentic changes give scientists clues to the age of a genome,” Ideker explains. “Just like wrinkles on a person’s face betray a person’s age.”

The researchers drew up a graph that accurately compares the age of american actor Tom Hanks to that of a cute labrador (see below). The method is based on a single breed of dog. And this is despite the fact that some breeds of dogs have a longer life than others. Although more research is needed, Ideker predicts that there is a good chance that the method will apply to all dog breeds.

Thanks to this study we now have a better picture of the aging process of dogs. And that’s important. “Vets often still use the old ratio of 1:7 years to calculate how old the dog is in human years,” says Ideker. “This information is then used to draw up decisions and treatment plans.” And this can now be done many times more accurately with the scientifically based method.

The researchers now plan to test the method on other dog breeds as well. In the meantime, Ideker – and maybe you now too – looks at his dog a little differently. “I have a six-year-old dog,” he says. “She still runs with me happily. But I realize now that she’s not as young as I thought she was.”