An old adage exists that every year your dog ages is equivalent to seven human years. Thus, a one-year-old dog is roughly the same age as a seven-year-old human, and a ten-year-old dog is roughly equal to a seventy-year-old human. This actually works really well for general terms, but have you ever noticed that bigger dogs seem to age a little faster than little dogs (i.e., eight-year-old Rottweilers seem to “act” older than eight-year-old Miniature Poodles)? The other issue is that even in the same size category, some pets of similar age seem to be older than others – just like in humans, in which we see some 70-year-olds running marathons whereas others have much less stamina at that age. Genetics and DNA (and breed in a dog’s case), lifestyle, diet, and ongoing diseases (such as heart disease, cancer, arthritis, etc.) all factor into the “physiological” age of humans and animals, which is another way of saying how old the body is compared to the number of years we have been alive.
Animals in general tend to develop much faster than humans because, instinctively, they must be ready to survive in the wild. A lot of what a puppy can do at the equivalent age of a human is going to be a bit more advanced. For example, puppies can crawl almost immediately after birth. As far as brain development goes, humans may take a little longer to develop, but we tend to be able to learn, retain, and understand much more than a dog ever will. Between physical and brain development, estimating equivalent ages between humans and puppies is a little tricky. Compare some of the common development milestones below:
Puppies: 0-3 days
Humans: Around 6 months
Puppies: 5-7 days
Humans: Around 1 year
Puppies: 4-6 weeks
Humans: Often much later (as early as 6 months-1 year)
Understanding or recognizing words
Puppies: 8 weeks
Humans: 9-12 months
Following simple directions
Puppies: 8 weeks
Humans: 9-12 months
Puppies: 6-16 weeks
Humans: 2-3 years
Growth plate closures
Puppies: By 18 months-2 years
Humans: By 14-16 years
*These are averages at best and meant to be used for comparison purposes.
So where does that leave us? Averaged together for both brain and body development, a two-month-old puppy is probably about the same age as a one-year-old human. At one month, he is probably closer to a six-month-old human. At four months old, he is probably roughly the same age as a two or three-year-old human. This will depend a little bit on the breed and size of the dog. Some dog breeds develop more slowly than others (physically, mentally, or both), but just like with humans, everybody pretty much catches up to each other eventually. After about six months of age, puppies slow down in their growth and development. They reach canine puberty at six months to one year of age, so a one-year-old dog is roughly the equivalent of a twelve-year-old human physically, with similar stamina, energy, and emotional maturity. Dogs will typically have reached their full size at around 18 months to 2 years of age. This is similar to around a 15-year-old human, give or take several years.
As you can see, aging varies a bit with young dogs, not quite following the “seven year” rule. Estimating age gets a little less complicated with adult dogs, other than accounting for breed and size. Historically, larger breed dogs and larger-framed dogs live an average of 10 years, whereas smaller breed dogs and smaller-framed dogs live an average of 14 years.
This rather large difference in aging among sizes and dog breeds has been studied by many scientists. The major reason found is that larger dogs literally age faster than smaller dogs. One study went so far as to say that for every 4.4 pounds of body weight a dog has, his life expectancy is decreased by 1 month. Essentially, because big dogs age faster, this means that a 10-year-old large dog is the same physiological age as a 14-year-old small dog.
Now consider the average life expectancy of a human, which is around 80 years of age. The 10 year old large dog and the 14 year old small dog are essentially both 80 year olds in human years. After a little mathematics, we can estimate rough ages for the different size categories: for every year of age into adulthood, a larger dog ages about eight years in human years, and a smaller dog ages roughly six years. Thus, an otherwise healthy six-year-old Labrador Retriever would be the equivalent of a forty eight-year-old human, and an otherwise healthy six-year-old Yorkshire Terrier would be the equivalent of a thirty six-year-old human. This doesn’t quite match up with the “seven year” rule, but it’s pretty close.
Age is Just a Number
Estimating human age is just that, an estimate. Nowadays, all dogs, both mixed breeds and pure breeds, are living longer because of the advances in veterinary medicine. Equally important, pet owners are making better efforts to keep their pets healthy with diet, exercise, and overall care. As a veterinarian, I know many 15-year-old large dogs, and they certainly don’t act like they are 120-year-old humans! The most important point is, regardless of how old you, your vet, or your dog thinks or feels he is, age is just a number. While there are no guarantees, doing whatever you can to keep your pet healthy and happy is the ultimate key to their longevity.