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Written by Paul
Dr Paul Manktelow is a vet who’s worked for almost 20 years on the front line in some of the UK’s busiest veterinary hospitals. As Chief Vet in the Charity Sector, he leads a team of vets and nurses that treat thousands of pets every year. Paul also appears regularly in the media as a TV and radio presenter, writer, public speaker and podcast producer.
We’ve all heard it: one dog year equals seven human years. It’s been repeated for so long it’s become “fact”.
But here’s the truth – it’s completely wrong.
Dogs don’t age in a straight line the way we do. They rocket through their early years and by the time you know it, that little puppy on your sofa is already middle-aged in human terms.
Where the 7-Year Rule Came From
This rule likely started with basic maths: humans live around 70 years and dogs live about 10. But life isn’t that simple. Dogs grow and develop much faster when they’re young, and then the process slows down.
When scientists at UC San Diego studied dog DNA, they found that a one-year-old dog is biologically closer to a 31-year-old human. By two years, they’re about 42. By age five, they’re already the equivalent of 57.
So the 7-year rule doesn’t just oversimplify things – it can make us underestimate how quickly dogs move through their life stages.
A Better Way to Calculate
You don’t need a complex formula to work out your dog’s age in human years. A simple guide is:
- First year = 15 human years
- Second year = 9 human years
- Each year after that:
- 4 human years (small breeds)
- 5 human years (medium breeds)
- 6–7 human years (large and giant breeds)
This matters most for large breeds, who can be considered seniors as early as six or seven.
Why It Matters
Knowing your dog’s true age isn’t just a fun fact. It helps you adapt their care as they grow older.
Senior dogs may need more regular vet checks, diets to support ageing joints and organs, and gentle adjustments to exercise. The sooner we make those changes, the better chance we have of keeping them happy and healthy for longer.
So the next time someone says “just multiply by seven,” you’ll know better. Skip the myth and think about where your dog is in their life stage – because understanding that could add precious years to their life.
Listen for More
I dig into this topic in detail in my latest episode of The Consult Room: How Old Is Your Dog in Human Years? Why the 7-Year Rule Is Wrong.
🎧 Listen to the episode here
