January 01, 2020 Dogs

How to Calculate Your Dog’s Age

A small brown dog lying in a bed wearing glasses

How to Calculate Your Dog’s Age

Happy New Year! As we ring in 2020, our thoughts often turn to being a year older and hopefully a year wiser. Dogs are a calendar year older too, but when the clock strikes 12am on New Year’s Eve, is your dog toasting to a new year or seven new years? Unfortunately, the answer isn’t quite so easy. In this blog post, we’ll look at some more sophisticated ways to determine your dog’s age.

One human year doesn’t equal seven dog years

The “dogma” about dog age is one human year equals seven dog years. The origins of this formula are unclear, but it’s possibly based on average lifespan, which is about 10 years for a dog and 70 years for a human. The math is easy, but if you think about it logically, the formula is just plain wrong. A one-year old dog can have a litter of puppies. According to the formula, this new dog mom would be seven years old! On the other end of the spectrum, Maggie, the world’s oldest dog, died at age 30, which would be 210 in human years. We clearly need a better formula.

Higher math for determining dog age

In 1997, researchers at Purdue University’s College of Veterinary Medicine developed a better formula by studying body weight, breed and age at death of over 25,000 dogs.

They created a formula to transform dog age to human age = {[(-0.0013 x X) + 0.0221]C3 } + {[(X x -0.0283] -0.1071]C2} + {[(0.2911 x X) + 4.9979] C} + (-3.6437 x X) + 37.423.

Where X is the median age of death for that breed or size of dog.

Where C is the chronological age of the dog in years.

Not very practical for the average dog owner, but if you happen to have a degree in computer programming, then figuring out your dog’s age will be a snap! However, this formula makes way more sense from my veterinary standpoint. It’s common knowledge in the dog world that large dogs and large breed dogs have shorter lifespans than small dogs and small breed dogs.

Back to the world’s oldest dog Maggie — she was an Australian sheep dog, or Kelpie, with an average size of 35 pounds. Using the information provided in the Purdue University study, Maggie’s age in human years would be estimated at around 105 or 106 years. That is a believable number.

Dog age as determined by DNA age

As living creatures age, their DNA ages as well. The age of a person’s DNA can be measured by chemical changes in the molecule that don’t change your DNA sequence but can affect your health and longevity. These changes are called “epigenetic” changes. A newly published study looked at epigenetic changes in Labrador retrievers up to 16 years of age and matched them to epigenetic changes in humans of various ages.  

From this data, the authors created yet another formula requiring high level math for calculating dog age in human years.  

16 ln(dog age) + 31.

(That’s the natural logarithm of the dog’s real age, multiplied by 16, with 31 added to the total.)

To avoid the need for a multifunction calculator, I used the convenient dog age calculator in this article (scroll down to find it) and determined, Maggie, the world’s oldest dog at 30 years would have been 85 human years old. Intuitively, that calculation seems low to me. These days an 85-year-old human is not that remarkable and you don’t get a special letter from the president until you hit 100. At AMC, we commonly see dogs that are 15-17 years old. According to the dog age calculator, they are 75-76 human years, which roughly matches the current average lifespan in the United States of 78-79 years. To me, Maggie should be more like 100 human years old and maybe the answer to dog age in human years cannot be extrapolated from DNA age.

Which ever method you use to calculate your dog’s age, times 7, based on size or his DNA age, all of us at AMC toast to a happy and healthy 2020 for all!