Is 1 Dog Year Really The Same As 7 Human Years?

Working out how old your dog is in human years is simple, right? You just multiply their age by seven, and Bob’s your uncle, you’ve got your answer. Turns out, however, it’s not quite as simple as that.

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There’s no denying that the whole “one dog year = seven human years” idea is persistent, but when you stop and think about it for a moment, it doesn’t really make all that much sense.

“In terms of how physiologically mature a 1-year-old dog is, a 9-month-old dog can have puppies. Right away, you know that if you do the math, you don't just times seven,” said Trey Ideker, a professor at UC San Diego School of Medicine and Moores Cancer Center, in a 2020 statement.

So if that formula isn’t right, is there one that is? To find out, we’ve got to take a look at what Ideker had been working on prior to 2020.

He was one of several scientists who had previously investigated the so-called “epigenetic clock”. It’s a tool that aims to measure biological age based on the pattern of DNA methylation, a process in which chemical “tags” known as methyl groups attach to DNA, altering its expression without changing the underlying sequence.

Ideker had been looking at its use in humans. Then, one day, his colleague Tina Wang came to him with a proposal – why not use epigenetic clocks to study aging in dogs?

“We always look at humans, but humans are kind of boring,” said Ideker in another statement. “So, [Wang] convinced me we should study dog aging in a comparative way.”

And that they did, carrying out a study that looked at the methylation patterns of 104 dogs – mostly consisting of Labrador retrievers – aged between just over 1 month to 16 years old at the time. The team then compared these patterns to those of 320 adults aged between 1 to 103 years old.

The work revealed that molecularly, dogs age much more rapidly initially, before slowing down at around the age of 7. With this data, the team developed a new formula for determining a dog’s age in human years: 16 ln(dog age) + 31. Definitely not quite as simple as multiplying by seven, but that’s what the ln button (referring to the natural logarithm of a number) on a scientific calculator is for.

Based on that formula, while a puppy that’s 8 weeks old would be considered the equivalent of a 9-month-old human, by the time that same dog reaches a year old, they’d be in their early 30s – quite the jump.

There are still questions left unanswered, such as whether the formula applies to other dog breeds too. But for now, maybe go easy on your pup if they’ve just hit the 7-month mark – they’re now basically in their 20s, and we all know what a rollercoaster that can be.