Most dog owners hope that their pet will be the one to defy the odds and live forever.

Sadly, our furry companions are not immortal.

And it turns out we’ve all been calculating our beloved pets’ actual ages incorrectly for years. The popular method of multiplying a dog’s age by seven to determine their human age has been proven wrong.

The first year of a dog’s life is actually equivalent to 15 human years, according to the American Animal Hospital Association.

And, how exactly a dog ages is different across breeds and sizes.

Here’s a look at how dogs age and what you can do to help yours live a long and healthy life.

Dog Years to Human Years by Size

Myth: Why 1 Human Year Doesn’t Equal 7 Dog Years

It’s hard to pinpoint where exactly the flawed myth of 1 dog year equals 7 human years originated.

“Part of the reason it is flawed is that a fixed ratio doesn’t account for the size differences among dogs; typically, smaller breed dogs live longer than larger breed dogs,” says Dr. Wendy Hauser, D.V.M., founder of Peak Veterinary Consulting and advisor to ASPCA Pet Health Insurance.

A 2013 study of 74 breeds of dogs examined the relationship between size and mortality. Researchers concluded that the reason large dogs die at a younger age is mainly because they age faster than smaller dogs.

“Dog aging isn’t a perfect science and isn’t even the same from dog to dog … Dogs mature more quickly in their first few years of their life, compared to later years, so all years are not equal,” says Nicole Ellis, certified professional dog trainer and pet lifestyle expert with Rover.

“It is believed this myth came to help pet parents understand the importance of yearly vet visits by showing that our dogs age much faster than us and hence a lot can change in a year and routine visits to your vet are important,” Ellis adds.

How Do Dogs Age?

The American Animal Hospital Association recognizes five age-related stages in the life of a dog:

• Puppy: Birth to 6-9 months (end of rapid growth); depends on breed and size
• Young Adult: 6-9 months to 3-4 years (completion of physical and social maturation)
• Mature Adult: 3-4 years to beginning of the last 25% of estimated life span; depends on breed and size
• Senior: Last 25% of estimated life span to end-of-life
• End-of-life: The terminal stage; depends on specific pathologies

“Your dog’s aging process is similar to your aging process but it happens faster,” says Dr. Heather Berst, D.V.M., medical lead Zoetis, which produces medicine and vaccines for pets and livestock.

“In just one year, you can notice your dog going from running and playing to slowly getting up from osteoarthritis pain. You usually notice your dog aging from their muzzle going grey, changes in vision and slow getting around,” Berst adds.

Scientists and researchers are making efforts to better understand how our dog’s age. A team of medical and veterinary medical experts across the country recently unveiled a more accurate method for measuring the physiological age of Labrador retrievers based on their genetic information. However, the scientists note it’s still unclear how this formula might apply to different breeds and sizes of dogs.

How Long Dogs Usually Live by Size

How long a dog lives depends on a great number of factors, including:

• Breed and size
• Diet
• Healthcare provided
• Lifestyle
• Activity level

The oldest dog on record is Bobi, a purebred Rafeiro do Alentejo, a Portuguese breed of livestock guardian dog. Bobi lived to be 31 years and 163 days old before passing in Oct. 2023.

Related: Human Years To Cat Years Calculator

When Are Dogs Considered Seniors?

When a dog is considered a senior varies by breed and size.

“Life expectancy is also highly breed dependent,” says Dr. Jean-Pierre Lautier, D.V.M. veterinarian and pharmaceutical manager for pet care company AB7 Group/Alzoo.

“Large and giant breeds generally have a low life expectancy, around 8 years. They enter the ‘senior’ category at around 7 years of age, at which point they require closer veterinary supervision,” Lautier adds.

Because large breed dogs tend to have shorter life spans, the AAHA notes that dogs are considered senior when they reach the last 25% of their estimated life span for their breed.

This translates to the following:

• Small or toy breeds (less than 20 pounds): 8 to 11 years
• Medium breeds (20 to 50 pounds): 8 to 10 years
• Large breeds (50 to 90 pounds): 8 to 9 years
• Giant breeds (more than 90 pounds): 6 to 7 years

How Owners Can Help Their Dogs Live Long, Healthy Lives

To help ensure your dog lives a long and healthy life, owners should practice the following:

• Regular physical exams: Puppies and young adult dogs should receive a complete physical exam at least once a year. Healthy mature adult and senior dogs should be taken to the vet at least twice a year.
• Preventative care: This includes vaccinations and parasite control. It’s important to stay up to date on vaccinations to keep your dog safe.
• Dental care: Poor oral health can lead to chronic pain and infection. Dogs need regular at-home teeth brushing, as well as periodic professional dental cleanings.
• Exercise: All dogs need proper exercise that goes beyond short walks around the backyard.
• High-quality diet: Be sure to feed your dog a high-quality diet that is appropriate for their age and breed to ensure they are receiving the proper nutrition for their growth.
• Weight control: Canine obesity has reached epidemic proportions. Canine obesity can lead to skin infections, orthopedic conditions, respiratory disease, diabetes and hypothyroidism.
• Pet insurance: Many dog owners purchase pet insurance to help offset the cost of regular vet visits, and cover the costs of any accidents or major illnesses that should arise.

Editor’s note: This story has been updated to correct the spelling and title of Dr. Jean-Pierre Lautier, D.V.M. veterinarian and pharmaceutical manager for pet care company AB7 Group/Alzoo. We apologize for this error.

Additional editor’s note: This post has been updated to reflect the passing of the oldest dog on record, Bobi.