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

The ‘1 human year = 7 dog years’ myth

It’s hard to pinpoint where exactly the myth of one dog year equals seven human years originated. But, today, experts claim that it’s flawed on the basis that a fixed ratio doesn’t account for the size differences among dogs. And, typically, smaller breed dogs live longer than larger breed dogs.

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.

Of course, dog ageing also is not 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.

How do dogs age?

The American Animal Hospital Association recognises 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.

A dog’s ageing process is similar to our own, but just happens faster. In just one year, you may notice your dog decline from running and playing, to slowly getting up from osteoarthritis pain. Other signs of ageing may include your dog’s muzzle going grey and changes in vision.

Scientists and researchers are making efforts to better understand how our dog’s age. A team of medical and veterinary medical experts across the US 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.

The table below sets out typical lifespans of dogs by breed size.

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

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

The current oldest dog on record is Bobi, a purebred Rafeiro do Alentejo, a Portuguese breed of livestock guardian dog. Bobi turned 31 in May 2023.

When are dogs considered old?

When a dog is considered a ‘senior’ varies by breed and size. Life expectancy is also highly breed dependent. Large and giant breeds generally have a low life expectancy, around eight years. They enter the ‘senior’ category at around 7 years of age, at which point they require closer veterinary supervision.

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 check-ups: Puppies and young adult dogs should receive a complete physical examination 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 back garden
• 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 is on the rise. 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.