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Dog Years to Human Years Explained

Candiece Cyrus
Forbes Staff

Updated: Apr 18, 2024, 2:19pm

Johanna Leggatt
editor

Edited By

Editorial note: Forbes Advisor Australia may earn revenue from this story in the manner disclosed here. Read our advice disclaimer here.
Dog Years to Human Years Explained

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Australia is a nation of pet lovers, particularly when it comes to dogs. Some 48% of households owned at least one dog in 2022, up from 40% in 2019, according to a 2022 survey of pets and people.

Many choose canines for their loyalty, intelligence and the love that they display, but dread to think about their short lifespans in comparison to humans’. At best, a dog will usually only live to around 20 years of age.

All the more unsettling, is recent research from the American Animal Hospital Association. It reveals we’ve been calculating our canine companions’ ages incorrectly for decades, by multiplying their years alive by seven to determine the human equivalent. The research reveals the first year of a dog’s life is the same as 15 in human years, and suggests a dog’s specific breed and size contributes to how it continues to age, with larger dogs maturing quicker.

However, this research should not be considered in isolation. As is typical of science, researchers are always finding new data that challenges the old, as is the case with the experts at the University of Adelaide. This year, they found that rather than ageing quicker, larger dogs typically die earlier than their smaller counterparts as a result of cancer caused by selective breeding for size.

We explain how dogs age, and how you can help yours live a long and healthy life below.

Dog Years To Human Years By Size


Human Years Dog Years <20 Pounds Dog Years 21-50 Pounds Dog Years
51-90 Pounds		 Dog Years >90 Pounds
1 15 15 15 15
2 24 24 24 24
3 28 28 30 32
4 32 33 35 37
5 36 37 40 42
6 40 42 45 49
7 44 47 50 56
8 48 51 55 64
9 52 56 61 71
10 56 60 66 78
11 60 65 72 86
12 64 69 77 93
13 68 74 82 101
14 72 78 88 108
15 76 83 93 115
16 80 87 99 123
17 84 92 104 –
18 88 96 109 –
19 92 101 115 –
20 96 105 120 –
Source: American Animal Hospital Association

The 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.

Continued research in this area over the years has provided new revelations. 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.

However, 10 years later, research from the University of Adelaide suggests otherwise. After investigating the causes of lifespan differences and death in 164 dog breeds, which ranged in size from Chihuahuas to Great Danes, the experts concluded that larger dogs were more likely to die from cancer at a younger age.

“Larger dogs didn’t necessarily age faster than the smaller breeds, but the research did show that as the breed’s average body weight increased, so did the rates of cancer,” said Dr Jack da Silva from the university’s School of Biological Sciences.

“We believe the relationship between a dog’s body size and their lifespan may be caused by an evolutionary lag in the body’s cancer defences, which are unable to keep up with the rapid and recent selective breeding of bigger dogs.”

The findings support a theory of ageing known as life history optimisation or the ‘disposable soma’. It’s based on the idea that all organisms prioritise growing and reproducing early, over maintaining health and a longer life. While concentrating resources on the former, an organism cannot focus on cell repair and cancer defences.

However, It’s not all doom and gloom for big dogs and their owners. Most of the 400 dog breeds have only been in existence for the past 200 years. The doctor expects the larger of these canines to eventually evolve to live longer lives, and instead have smaller litter sizes, either naturally or through selective breeding of larger dogs with lower cancer rates.

How Do Dogs Age?

According to the American Animal Hospital Association’s findings, all dogs, regardless of size, mature more quickly in their first few years of their life, compared to later years, so all years are not equal.

The 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 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.


Breed Size Average Life Span
Small or Toy Breed (less than 20 pounds) 10-15 years
Medium Breed (20 to 50 pounds) 10-13 years
Large Breed (50 to 90 pounds) 8-12 years
Giant Breed (more than 90 pounds) 8-10 years
Source: American Kennel Club

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

  • breed and size
  • diet
  • healthcare provided
  • lifestyle
  • activity level.

The world’s oldest dog on record was Bobi, a purebred Rafeiro do Alentejo, a Portuguese breed of livestock guardian dog. He died aged 31, in October 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.

In Australia, many dogs are deemed senior by pet insurance providers when they reach the age of nine, which means that a new policy cannot be taken out once the dog reaches this age.

How Owners Can Help Their Dogs Live Long, Healthy Lives

To help ensure your dog lives a long and healthy life, owners should practise 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, orthopaedic 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.

Physiotherapist Kristine Edwards and veterinarian Hendrika Tegelaar, say it’s a misconception that it’s normal for dogs to move less, get stiff and sore with age on the Dogs Australia site. As with humans they can be elderly yet happy, comfortable and healthy. They advise looking out for signs of your dog maturing and taking action from as early as possible.

Frequently Asked Questions (FAQs)

What are the signs of a dog ageing?

As with humans, signs of ageing are varied in dogs.

They may experience:

  • Changes in physical appearance: this can range from grey fur in their coat, to calluses on their elbows
  • Weight gain: As dogs get older, their metabolism slows, which can lead to weight gain and obesity
  • Poor health: a dog may develop a dental disease. It may also develop heart disease, respiratory problems and decreased liver function. These may be diagnosed by your vet.
  • Changes in vision: including a condition called nuclear sclerosis which causes the lens of the eye to appear cloudy, while the dog maintains quite good vision. It is not to be confused with cataracts, the clouding of the lens area of the eye, which can hinder vision, or glaucoma which is damage to the optic nerve
  • Hearing loss: owners may identify hearing loss if their dog no longer follows commands or seems aggressive when they approach. This may be because they were taken by surprise. Owners can help their dogs by teaching them some signed commands.

What are the most popular dog breeds in Australia?

According to Dogs Australia National Registration Statistics for 2022, the most popular dog breeds are:

Out of all breed groups:

  1. Labrador Retriever
  2. Golden Retriever
  3. Staffordshire Bull Terrier

Toy group:

  1. Cavalier King Charles Spaniel
  2. Pug
  3. Italian Greyhound

Terrier group:

  1. Staffordshire Bull Terrier
  2. American Staffordshire Terrier
  3. Jack Russell Terrier

Gundog group:

  1. Labrador Retriever
  2. Golden Retriever
  3. Cocker Spaniel

Hound group:

  1. Whippet
  2. Rhodesian Ridgeback
  3. Dachshund (Min. Smooth)

Working dog group:

  1. Border Collie
  2. German Shepherd Dog
  3. Australian Shepherd

Utility group:

  1. Schnauzer (Miniature)
  2. Rottweiler
  3. Boxer

What is Australia’s oldest dog?

Up until its death in 2016, Australia’s oldest dog was also thought to be the world’s longest living dog, though not officially recorded. It was Maggie, a Kelpie, that lived on a dairy farm in Victoria. It’s thought the dog was 30-years-old when it died.

Official records show the world’s second-longest living dog to have lived in Australia. The Guinness World Records says it was Bluey, an Australian Cattle Dog, which died aged 29 in 1939.

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Candiece Cyrus Forbes Staff

I have been writing for newspapers, magazines and online publications for over 10 years. My passion is providing, in a way that is easily accessible and digestible to all, the knowledge needed for readers to not only manage their finances, but financially flourish.