Dog years vs. human years
Old beliefs and urban myths
Beliefs have a way of
transcending generations. Everyone has heard that one year in the life of a dog is equal to seven human
years. This 7:1 aging ratio was the standard rule of thumb for many years. Times have changed, but this
old formula still lingers on
and persists despite modern research and new truths. You
are just as apt to hear this today as you were 50 years ago. Is this simply an old wives tale or an urban
myth? Where
did this formula come from? Does it have any basis in fact? Does it really matter?
It is very likely that this equation is rooted in the truth of the ages and that it was developed at a time
when the comparison was accurate. In all likelihood, the 7:1 ratio was based on the assumption that a
dog
lived for approximately 10 years and a human for about 70. At that time, the "average"dogs being
looked
at were in all probability medium-sized farm or yard dogs (Retriever, collie, and shepherd sized dogs).
The sampling of dogs considered may have been primarily outdoor dogs as opposed to indoor pets.
We
may never know the exact criteria and origin, but whatever the source and science, at the time 7:1
appeared right and it stuck.
Whether there is a direct comparison of dog years to human years does not matter one whit to our
canine
companions, but it matters to us. It is human nature to want to know about the world, and to try to
discern
similarities between ourselves and the animals that share our lives.
Old beliefs and urban myths
Beliefs have a way of transcending generations. Everyone has heard that one year in the life of a dog is equal to seven human years. This 7:1 aging ratio was the standard rule of thumb for many years. Times have changed, but this old formula still lingers on and persists despite modern research and new truths. You are just as apt to hear this today as you were 50 years ago. Is this simply an old wives tale or an urban myth? Where did this formula come from? Does it have any basis in fact? Does it really matter? It is very likely that this equation is rooted in the truth of the ages and that it was developed at a time when the comparison was accurate. In all likelihood, the 7:1 ratio was based on the assumption that a dog lived for approximately 10 years and a human for about 70. At that time, the "average"dogs being looked at were in all probability medium-sized farm or yard dogs (Retriever, collie, and shepherd sized dogs). The sampling of dogs considered may have been primarily outdoor dogs as opposed to indoor pets. We may never know the exact criteria and origin, but whatever the source and science, at the time 7:1 appeared right and it stuck. Whether there is a direct comparison of dog years to human years does not matter one whit to our canine companions, but it matters to us. It is human nature to want to know about the world, and to try to discern similarities between ourselves and the animals that share our lives.HUMAN LONGEVITY -
A look through history shows that the average life expectancy of mankind in
the past has tended to be quite short; our caveman ancestors with a scant 20-25 years, very gradually
increasing through millennia to about 35 years in
early 18
th
century England and advancing to 50 years
by the early 20
th
century. The 20
th
century saw the
greatest changes, with average human life expectancy
increasing decade by decade until the present. The
current average in North America, as per 2008
calculations, is 78 years in the USA and 80 years in
Canada. 
The graph shown here is not from scientific
study; it is simply a rough timeline for illustration
only. Keep in mind that life expectancy from birth is
not a direct measure of anticipated longevity. There
are always individuals that live longer or shorter than
the average. Those that live to exceptional ages are balanced out by those who live only a very short
time.
The average is between the two extremes. This is one reason why average human life expectancy was
so
low in the past. Many babies did not survive infancy or childhood; plagues wiped out entire
populations,
wars disseminated countries, etc. Some individuals did live to see advanced years, but so many died at
younger ages for assorted reasons that the average remained very low. The sharp trend to increased life
expectancy from the 18
th
century onward in large part stems from improving sanitation, better nutrition and medical advances.
Further increases in lifespan may be expected in the future. Though this may appear to be a meaningless
bit of trivia, it is in fact very important. The same changes that affected the lives of humankind also had
an effect upon our animal companions. The clean water, good food, vaccinations and treatment for
illnesses which made an indelible impact on our lives, increased the life expectancy of domesticated and
companion animals alongside our own. While human life expectancy has been documented and studied
through the years, data for animals is much harder to find. That brings
us back to the famous or infamous 7:1 ratio. It may not be the first such equation but it is certainly the
most well known and likely originates somewhere around the mid 20 th
century (when the human life
expectancy was approximately 70 years).
New theories
In reality, 7:1 does not give the whole picture, nor is 10 years an accurate average. There is considerable variation in the lifespan of the dogs who share our lives. Most medium sized dogs, if well cared for, will live for an average of 10 to 13 years. Small breeds, on the whole, extend this span by another few years while large and giant breeds diminish it similarly. Knowing the life expectancy of your chosen breed will give clues of what to expect in dog years, but we still come back to the question of "How old is my pet in human years?"Many factors need to be taken into consideration in determining this which means that there is no single simple equation to calculate the relative human age of your pet. Even so, all is not for naught. Modern comparison charts can help you easily find out approximately how "old"Sonni is.
The old 7:1 formula would have you compare a 6 month old dog to a 3&1/2 year old child, a 1 year old dog to a 7 year old child and a 2 year old dog to a 14 year old teen. Like in humans, there are many stages of development throughout the life of a dog. A dog's development from birth through puberty and on to adulthood takes place over a very short period of time, only about two years as compared to approximately 21 years in humans. Life stage comparisons show that a 6 month old puppy is closer to a 8-10 year old than a toddler; a one year old dog closer to a pre-teen or teenage youth than an elementary school aged child and a two year old dog closer to an adult than to a teenager. For most breeds, a one year old dog has reached most or all of its physical height and has also reached sexual maturity, but may still have some muscling up and filling out to do(comparable to a human teen). Another year fills in the space of a teen maturing into a young adult. For small/medium dogs, birth to adulthood may take 15 to 24 months. For large and giant breeds, it may take 20 to 30 months. Full maturity may take another few years. In dogs, the rate of aging slows down dramatically after the first year or two. Even after this initial period of rapid development, a dog does not age 7 years per calendar year; in these subsequent years, canine aging is perhaps more closely related to 4:1 to 6:1 for most breeds. For large and giant breeds and for other breeds with a life expectancy of less than 10 years, 7:1 and 8:1 ratios may be more accurate. There is not a one-size-fit all formula. Rates of aging also depend on breed, size, body shape and other factors. Human/canine conversion charts based on comparable life stages and development are much more realistic than a base ratio. The chart below is my own, which has been compiled from my personal research, canine aging studies and general breed life expectancy data. The comparison is based on the average human lifespan of 80 years. There are many such charts to be found. Most will be similar but there can be differences.
To use this table, use the top row to find your dog's type according to the life expectancy of its
specific
breed. In the left hand column, find your dog's actual age. The spot at which the two intersect is the
approximate age in human years. The comparable steps in the stages of human life are:
- 1) Childhood/Youth from birth to 20 years of age
- 2) Adult (prime) from 21 to 45 years of age
- 3) Mature adult (middle age) from 46 to 65 years of age
- 4) Senior from 66 to 85 years of age
- 5) Senior Plus spans 86 to 100 years of age; above the average north-american life expectancy.
- 6) Centenarians, over 100 years of age, are occuring with increasing frequency but still represent a very low percentage.
- 7) Extraordinary long lives are those who survive to 120 or more years ... only a handful throughout the world.
There is more value to this determination than just the fun of knowing how old your dog is compared to the humans in your family. By relating the stage of a dog's life to our own, we can better understand our canine companions and their needs. The good news is that the changes of improving nutrition, and healthcare advances which improved our own life expectancy, have also improved that of our canine companions. Dogs today live longer than ever before. Remember, life expectancy is not a direct measure of anticipated lifespan; there will always be dogs whose lives are shorter or longer than the average. Not surprisingly, it is the exceptionally long lived dogs that we hear about in the media; however, these particular animals that live to 20 years of age and beyond are not typical of dogs as a species or of any breed in particular. Canine longevity studies estimate that less than 10% of all dogs live beyond 15 years. The Guinness World Book of Records lists an Australian Cattle dog named "Bluey" as the longest lived canine ever officially recorded, having lived to the ripe old age of 29 years and 5 months (1939). Even though our Havanese may not match Bluey for longevity; barring illness or accident, owners can look forward to a good long life for their beloved furry companions.