How the 7-to-1 Calculation Began

The dog age equation goes beyond simple mathematics. For example, many dogs reach sexual maturity around 1 year of age, and some even sooner than that. A human child is typically 13 or 14 before reproductive hormones start kicking in.

But with dogs, there are plenty of other factors to consider when it comes to longevity, including the breed of dog. For instance, a Saint Bernard is destined to have a shorter lifespan than the average chihuahua. With all the variables, it seems the theory of comparing dog years to human years can be rendered almost moot.

So, how did this generally accepted dog age calculator get started, anyway?

No one really knows for sure. There is an inscription dated 1268 in the Cosmati pavement in front of the High Altar of Westminster Abbey. The pavement was ordered by Henry III and refers to the end of the world. For some reason, the ancient text states that the health of an 81-year-old human would be equivalent to that of a 9-year-old dog. The vitality of a person that old may have been a guess since many people tended to live only into their 30s in those days.

But the popular 7-to-1 ratio was probably initiated by a 1700s French naturalist, Georges Buffon. The Count de Buffon theorized that since humans lived around 90–100 years and dogs lived 10–12 years, every dog year equaled about seven for a person.

Since then, the dog age calculator has been enshrined in society as dog years to human years equaling one to seven, respectively. The theory was so widely accepted that it was even included in math textbooks beginning in the 1960s.

Although the comparison may be generally accurate for the typical older dog, there are many different factors which prove the traditional dog age calculator to be inaccurate. A few of these include the facts that:

1) Many dogs live past the age of 15, which at the 7-to-1 ratio would put a person at 105. Dogs, in fact, have been known to live over the age of 20 (140 human years), and the oldest dog on record was 29 (or 203 human years). The oldest human, on the other hand, managed to stay around until age 122.

2) A 1-year-old dog is more of an adolescent than a 7-year-old human.

Dogs and Humans Do Not Age at the Same Rate

From birth until they reach their adult stage, dogs grow at a far more accelerated pace than humans do. A dog at 2 years of age is similar in maturity to a person in their mid-20s. Upon reaching that stage, a dog’s growth will slow down and level off to about 3–5 dog years for each human year.

French researcher A. Lebeau created a new calculation for the dog years to human years conundrum. Although that was in 1953, the 1- to 7-year ratio continued to dominate public thinking on the matter, probably because it was simpler in theory. But Lebeau calculated the age equation at a 4:1 ratio following the dog’s second year. However, Lebeau’s method didn’t take into consideration how some dogs reach old age at just 7 or 8 years. So, no known method for a dog age calculator can be truly accurate in the universal sense.