It’s a sad fact of life that our canine companions possess a much shorter lifespan than the average human. For this reason, the age and maturity of a seven-year-old dog is far different from that of a seven-year-old human.
Find out how you can calculate your dog’s actual age, plus the reasons why small dogs age slower and possess a longer lifespan than large dogs.
Is One Dog Year Equal to Seven Human Years?
There is a long-held theory that one dog year is equal to seven human years, but this theory is not fully backed by science. Instead, the “age” of a dog depends on several factors, including its size, breed, and lifestyle.
The 1:7 ratio has stood the test of time, and many people still use it to calculate their dog’s age, but the truth is not so straightforward.
This theory likely stems from common statistics. An average human would live to around 70 years of age, while a dog could expect a standard life of approximately 12 years. Still, William Fortney, a vet at the Kansas state university, told the Wall Street journal that this piece of information was more likely to have been designed as a marketing ploy.
From a health standpoint, highlighting the short lifespan of a dog could encourage their owners to visit the vet more regularly and keep a keener eye on their dog’s health.
How Do I Convert My Dog’s Age into Human Years?
Accurately calculating your dog’s age requires you to consider several factors.
According to the American Veterinary Medical Association, we can break a dog’s lifespan down as follows:
- The first year of a dog’s life equates to roughly 15 years of human life.
- The second year of a dog’s life equates to approximately nine years of human life.
- Each subsequent year equates to around five years of human life.
Say you have a seven-year-old dog; you could calculate an estimate of their age using the following calculation:
15 + 9 + (5 x (total number of years -2)
Or 15 + 9 + (5×5) which is 49.
Therefore, we can conclude that the average seven-year-old dog is about 49 years old. Now, you may realize that this perfectly fits with the 1:7 ratio (a much more manageable sum to complete), but a seven-year-old dog is the only age where this ratio sticks.
Using the AVMA calculation, we can estimate a dog’s age as the following:
| Dog Years | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Human Years | 15 | 24 | 29 | 34 | 39 | 44 | 49 | 54 | 59 | 64 |
Do Smaller Dogs Age Slower?
While the AVMA offers a framework to estimate your dog’s age, it is by no means a precise measurement. You’ll also need to factor in the canine size to obtain an accurate figure.
A small dog is considered a senior once they reach the age of seven, whereas a large dog can transition to a senior state as early as five to six years old. This classification of a “senior” dog is based on many behaviors related to old age (such as sensory or memory loss) that we may also equate to human “senior” traits.
One example of this is the Great Dane. According to the Great Dane Club of America, the life expectancy of this breed sits around seven to ten years old. That means that a Great Dane who is four years old would already be in their mid-thirties in human years.
As a rule, smaller dogs age more slowly than larger dogs, though you would need to check the breed specifications for your pup as some breeds are outliers to this data.
Why Do Small Dogs Age Slower?
The relationship between a dog’s body mass and its lifespan is a complex one that has puzzled scientists for years. As yet, there is still no research to provide a definitive answer to this question.
We know that large mammals, like whales and elephants, generally have a longer lifespan than smaller animals such as mice or rabbits. So, it’s baffling that large dogs would have a lower life expectancy than smaller ones.
Evolutionary biologist Cornelia Kraus stated that the life of a large dog “seems to unwind in fast motion.” The research conducted by Kraus and her team assessed whether large dogs aged faster and if large dogs experience an increased mortality rate throughout their lives, regardless of age.
The analysis indicates that large dogs age at an accelerated pace, with a strong correlation on the curve of the faster-aging hypothesis.
One theory why this could be the case is that large dogs have higher concentrations of the growth hormone IGF-1 in their blood than small dogs do. This increased level of IGF-1 has been associated with an increased risk of death across a number of species, including humans. But more research would need to be conducted to confirm this hypothesis.
