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Why ‘Dog Years’? The Truth Behind Canine Aging

The concept of a dog year in human years can provide light on the aging process. We’ve been adjusting the gap in average lifespan between dogs and humans by using dog years for some time now. Why do we do this?

Quick Answer

In a nutshell, we use dog years to compare human aging to dog aging. For example, a dog’s equivalent of one year is seven years. However, as the table below shows, this is only an overview, not a direct relationship.

Curiously, this way of equating dog age to human age has roots in early veterinary science, with the 7-to-1 rule simplifying the complex process of aging.

How Old Is Your a Dog in Human Years? Here’s a nice dog year conversion table for you:

Dog SizeSmall
20 lbs or less
21-50 lbs
51-100 lbs
100+ lbs
Dog AgeAge in Human Years
Source: AKC, How to Calculate Dog Years to Human Years

Note #1: The reason why it’s first 15 years, then +9, then all over the place is because the age relationship between a dog and a human varies depending on the stage of life and the dog breed. Also, dogs age faster when young and slower as they age.

Note #2: In addition, larger dogs tend to develop problems related to aging earlier than small dogs, and their overall lifespan is shorter.

As you can see, it’s no longer 7 for 1, more like 6.5 for one, depending on the breed and how old the dog is. We’ll get into this a bit further below.

short coated black and white puppy playing in sand

What Was the Idea Behind Dog Years?

While many attribute the dog year calculation to ancient civilizations trying to make sense of canine aging, its mainstream acceptance can be credited to more recent attempts to communicate a pet’s stage in life in relatable human terms.

The concept behind dog years is that since dogs have considerably shorter lives than humans, one year in a dog’s life is equivalent to many years in ours. The exact ratio varies depending on the dog type, although we once thought one dog year equaled seven human years.

This idea is frequently used to characterize a dog’s relative age. Because dogs have shorter lives than humans, it is a means of normalizing our differences.

Dogs age faster than humans. A one-year-old child is still considered a baby. A dog is typically mature at one year of age. A five-year-old youngster has a long way to go in terms of development. However, a five-year-old dog is as mature and grown up as ever.

You could argue that humans made up the concept of dog years to keep them from being sad that dogs die young. As with most cliches out there, this one is probably true. If you use 7 for dog years and your dog dies at the age of 12 (84 in dog years), you can say he had a good life.

Using dog years as a tool of comparison also acts as a gentle buffer, helping both children and adults emotionally process the shorter lifespan of their canine companions.

It’s also a method for us to convey to our children that just because the dog died when he was 12 doesn’t mean they will.

In the end, dog years are little more than a mechanism for humans to relate to them in terms of life expectancy. While dogs don’t seem to be aware of their age, we sure like to keep track.

Is It Really 7 for 1 or Something Else?

Dog years are a simple method for children to understand why their dog dies before them and for grownups to normalize the differences in aging.

The proportion works well. Most dogs survive until the age of 10-12, and most people live until the age of 70-86. Do dogs age seven times faster than humans? They do not.

It used to be that for every human year, there were seven dog years. However, this is no longer the case. As previously thought, each dog year does not equal seven years. Dogs and humans do not age at the same rate, and the rate of aging slows after six in dogs.

The bottom line is that dog years are an urban legend. It normalizes their age in comparison to people. However, it does not depict an accurate image of dogs. A female dog of 6 months can become pregnant and have puppies, but that is 3.5 years in human years. Does that make sense?

This is why we believe the first year of a dog’s life is worth more. In that period, dogs mature from newborn to adult. Therefore, the first year for a dog is equivalent to 12 to 15 years for people.

The idea that every dog year is equivalent to seven human years is a figure of speech that is incorrect. Both numbers are arbitrary, and the connection between them is not linear. The life spans of humans and dogs vary greatly.

golden retriever dog sitting on the ground outside during daytime

A more accurate way of looking at it is to compare a dog’s age and developmental stage to that of humans, yet even that varies from one person or dog to the next, and it’s not linear.

For example, smaller dogs have longer lifespans than larger breeds, so their years would be proportionately longer. The aging process of a dog can be influenced by genetics, nutrition, and exercise, making it impossible to compare it to that of a human.

In any case, the belief arose because dogs live roughly a human life span divided by seven for 12-15 years, depending on the breed.

How to Calculate Dog Years?

Determining a dog’s age in “dog years” is not an exact science and can change depending on the dog’s breed, size, and overall health. However, you can use a rough guideline to determine a dog’s age in human years.

One method is to use the following formula for small dogs:

  • The first year of a small dog’s life is approximately 15 human years.
  • The second year is about 9 human years.
  • After then, each year is four human years.

It’s similar for medium and large dogs, except that after age five, the following year equals 6 for medium and 9 for large breeds. After that, each year counts as 4 to 5 years for medium breeds and 5 to 6 years for large dogs.

Remember that these are estimations rather than scientific measures and that various breeds and individual dogs may age differently. Consult your veterinarian for a more precise estimate of your dog’s age.


Are cat years the same as dog years?

The concept of “cat years” is similar to “dog years” in that it estimates a cat’s age in relation to human years. For cats, the equivalent is dog years for a small breed, where the first two years equal 24 human years, and the following is +4 years.

Do dogs live longer today than in the past?

Dogs have been living longer today than in the past due to advancements in veterinary medicine and living conditions. Dogs have been living longer due to improved nutrition and diet, vaccinations and preventative care, better living conditions, and advancements in veterinary medicine.

How many dog days in 1 human day?

It is inaccurate to compare dog days to human days as dogs and humans age differently. The concept of “dog years” is a rough approximation and not scientifically accurate, and translating this to days is an almost impossible and usually incorrect way of calculating.

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