How to Calculate Dog Years and Cat Years

If you think you can calculate dog or cat years by multiplying by 7, think again. That’s the OLD way of doing the math.

How to calculate dog's age in human years
Happy birthday! Now, how do you calculate dog years or cat years? Photo: annmariephotography

I have always understood animal years are 7 times human years. I can’t remember where I picked this up, but it’s stuck with me for most of my life. If you had a dog for one year, they were 7 in dog years. Simple as that.

When you think about it, dogs and cats can start reproducing just months after they are born. Humans can’t reproduce that soon, so it made me wonder how this original calculation was formed.

That’s like saying a 1-year-old human can reproduce. Scary, huh?

Dog Aging

Dogs age pretty fast in their first couple of years, but the aging process varies depending on the breed.

  • Larger breeds such as Newfoundlands mature much more slowly but tend to have shorter life spans.
  • Medium and small dogs reach senior status much later in life, around 7 years of age for medium-sized dogs and 10 years for toy breeds.

While no true and exact method is available for calculating dog years, veterinarians agree that this is a much better guideline to follow instead of the one times seven method.

These new guidelines assume that a 1-year-old dog is equal to a 12-year-old human. The amount doubles after that (a 2-year-old dog is equal to a 24-year-old human), and continue this method adding 4 years for every age that follows.

This new method takes into account the earlier maturation and slowing toward senior years.

The director of veterinary services at Boston’s Animal Rescue League, Martha Smith, agrees that this calculation is a more accurate representation of dog years.

Here it is in chart form:

Calculate dog's age in human years

The average life span for dogs ranging in the low teens, but this can vary by breed. Large breeds tend to live shorter lives while medium and small dogs (and females) live much longer.

Cat Aging

The formula for calculating a cat’s age is a little different.

Here’s a chart to show how a cat’s age in human years is calculated:

Calculate cat's age in human years

Cats live an average of around 15 years (indoors) and 10 years or less (outdoors). Their first year is a little more maturing than dogs, but they catch up at year 2.

Looking over these charts has me thinking about my own pets. By these calculations, my dog is almost 64 years old and my cat is a spring chicken at around 15 years old.

I hope I look as good as my dog when I reach that age!


This pet health content was reviewed for accuracy by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed and updated Dec. 31, 2019.