We hate to be the ones to break it to you, but you can't calculate how old your dog is in human years by multiplying their age by seven.
It's not really clear where the idea came from, but it's one you'd probably heard quite a bit of by the time you hit the dog age of 49 in your first few years of elementary school. It's also a complete myth, and doesn't really give a good equivalent of what stages of life dogs and humans are at in relation to each other. For instance, a 1-year-old dog is generally fully grown, in a way that would be incredibly freaky for a 7-year-old human child. Dog lifespans also vary wildly, with smaller dogs (generally) living longer than their larger friends.
Fortunately, scientists have been hard at work to produce a more accurate measure, in order to help you find out whether your dog is a cheeky toddler or having a mid-life crisis. A team has published a pre-print paper on bioRxiv that attempts to come up with a better comparison of dog and human ages by looking at the DNA of both species.
As humans and other animals age, methyl groups are added to our DNA molecules, which can change the activity of a DNA segment without changing the sequence. This gives us a way of measuring age in humans, called the epigenetic clock. The team, led by researchers from the University of California, looked at the epigenetic clock of dogs and humans.
They looked at the methylomes of 104 Labrador retrievers spanning a 16-year age range in order to establish their "cross-species translator of physiological aging milestones".
"Comparison with human methylomes reveals a nonlinear relationship which translates dog to human years, aligns the timing of major physiological milestones between the two species, and extends to mice," the team writes.
The result is the following equation which – while not quite as catchy as the seven year myth – is a much better translation of ages between the two species:
human_age = 16 ln(dog_age) + 31
To get it you need to take your dog's age and find its natural logarithm (use this calculator for ease) and multiply it by 16, before adding 31. Voila, a dog-to-human age translator.
At the moment, of course, this is much more accurate if you have a Labrador retriever, and the researchers note that it works best for younger and older humans and dogs than it does for the middle ranges. Nevertheless, it's much more accurate than the way you've been taught so far.