Are ‘dog years’ accurate?

When it comes to assessing how old your dog is, most of us will fall back on the common misconception of dog years. In this calculation, every year of your dog’s life is worth seven in human terms. But is this an accurate way of assessing the relative age of your dog? According to the latest research, it is way off, with the real formula much more complicated. Whilst A&T Dogs provide a doggy day-care service, the team is becoming more aware of the characteristics between the dogs’ age groups.


Where did ‘dog years’ come from?

The formula for dog years comes from dividing the average lifespan of a human, around 77years, by the average lifespan of a dog, around 11years. Just reading that, you can see that it is not going to be true. Some dogs have been known to live long into their late teens, making them well over a hundred. What’s more, larger dogs are known to have a shorter lifespan than smaller dogs, further undermining the ‘dog years’ formula.


Non-linear development

Anyone who has dogs, or who works with them in dog kennels or doggy day-care, knows that dog development is not a straight line. Dogs mature fast from birth, developing teeth within eight weeks and reaching sexual maturity by around nine months. In humans, teeth don’t appear until around nine months and sexual maturity happens around age 12. Clearly, dogs mature rapidly at first, then slow down as they get older.


How should we count dog years?

Bearing in mind the non-linear aging, the American Veterinary Medical Association (AVMA) says that we should consider the first year of a dog’s life to be the equivalent of around 15 human years, the second year to be the equivalent of nine years and every year after that to be worth between four and five human years.


This fits with the ‘dog years’ theory when you consider a seven-year-old dog is 49 human years (7×7) under the ‘dog years’ approach and also 49 under AVMA formula (15+9+(5×5)), however, the important difference is the rate at which they get to this ‘age’.


How vets count dog years

Generally speaking, vets don’t tend to use an exact formula, preferring to put dogs into ‘life stages’ as follows, based on a life expectancy of 13 years:

  • Puppy stage – 0 to 9months – birth to sexual maturity
  • Adolescent stage – 9 – 12 months – sexually mature and still growing
  • Adult dog – 12months to 6years – finished growing, fully mature
  • Middle age – 6½ – 9½years – mid to late maturity
  • Senior dog – over 9½years – last quarter of average life
  • Geriatric – over 13 years – older than average life


Different breeds age at different rates

Even the simplified approach above has its problems, as different breeds age at different rates. Unlike most other animals, where larger creatures tend to live longer than smaller ones (think elephants vs mice), larger dogs have a shorter life expectancy than smaller ones. Research from Gottingen University in Germany found that every 4.4pound increase in body mass reduces a breed’s average life expectancy by around a month.





An alternative formula

A study of 104 Labrador retrievers by the University of California San Diego looked at genetic markers on the DNA called methylation markers, which correspond to aging in both humans and dogs. They found that a dogs age could be calculated using the following logarithmic formula:

Dog’s age in human years = 16 x ln(dog’s age) + 31years

This puts our seven-year-old dog at around 62 human years. This formula may be more accurate and based on genetic science, but for those of us who can’t do logarithmic functions (ln) in our heads, it’s probably easier to use the AVMA system of 15 + 9 + 5 + 5… etc.


Why does it matter?

Understanding how old your dog really is in human terms is not only fun, it’s important for their health and wellbeing. If you use the traditional ‘dog years’ formula, you can badly underestimate how old your dog really is, and not look after them appropriately or get them the right veterinary care.


When your pet comes to the dog kennels at A&T Trained Dogs, our dog minders and doggy day-care team will accurately assess how old your dog really is, including size and breed factors, and design care and activities that are appropriate for them and their life stage.