To determine your dog’s age in human years, you simply multiply his age by seven. This has been the universal formula used for many years, but it turns out it’s not as accurate as everyone thought it was. Researchers have found a new way to convert dog years to human years. Find out how old your dog is in human years using the new formula.
One Human Year is Not Equivalent to Seven Dog Years
The “dog years rule” is based on the myth that every year a dog spends in this world is equivalent to seven years for a human. No one knows where the 7 to 1 ratio originated from but an inscription in Westminster Abbey in 1268 seem to indicate a calculation based on a 9 to 1 ratio.
Although 7:1 ratio is widely used, it does not reflect the reality of short life span of humans. If the ratio is true, it would support the idea that humans can live for hundreds of years, which is not the case. Take the case of the world’s oldest dog who lived for 29 years, which is equivalent to 203 human years. This shows that the old formula is more of a random thing and not rooted in science.
William Fortney, a vet at Kansas State University, suggests that the 7:1 ratio may have been a marketing ploy to educate people on how ageing is quicker for canines compared to humans so that they are encouraged to bring their dogs to the vet at least once a year.
A More Accurate Approach
Researchers believed that they found a more accurate way of calculating a dog’s age by taking into account the evolutionary changes in both humans and dogs. As humans and dogs age, methyl groups attach to their DNA. This process is called methylation which allows for the tracking of biological growth and development of both humans and canines.
By measuring the methyl group accumulation in the DNA molecules over time, researchers can calculate the speed at which dogs and humans are ageing. Essentially, the process aligns the timing of physiological growth milestones between the two species.
The study matched the methylation profiles of Labrador retrievers between 4 weeks old and 16 years old with that of humans. From the data collected, researchers came up with a formula to determine your dog’s age that’s comparable to human age.
Formula: [Human age = 16ln(dog age) + 31]
Here’s how to use this formula:
- Enter your dog’s age in a scientific calculator to determine the natural logarithm of your dog.
- Take the number you derived in Step 1 and multiply it by 16 and then add 31.
- The result is your dog’s age equivalent to human age.
For example, your 5-year old Labrador retriever would have a natural algorithm of 1.6094379124341003. Multiplying that by 16 and adding 31, the age of your dog would be comparable to a 56-year old human.
Using the old 7:1 formula, your dog would only be comparable to a 35-year-old human. The discrepancy is mind-blowing because it tells you that your dog is actually ageing faster than you think.
Bear in mind that the study was done on Labrador retrievers only so the formula may not be accurate on other dog breeds, especially taking into account the fact that they age at different rates. Even with a margin of error, this new formula would be more accurate than the simple 7:1 ratio because there’s some science backing it.
Alternative Ways to Determine A Dog’s Age
1. Based on dog size and breed
Dogs grow more rapidly than humans at every comparable stage of development from birth to childhood. The American Veterinary Medical Association (AVMA) has created a general guideline to estimate a dog’s age based on how fast they grow taking into account the size and breed.
- A one-year-old dog is equivalent to 15 human years (14 for large and giant breeds)
- A two-year-old dog is comparable to a 24-year old human (2-4 years less for large and giant breeds)
- After the second year, the dog ages 3 to 5 dog years per human year depending on factors such as breed, size, and health condition, among other things.
The size and breed of your pooch also play an important role in determining his age. It is known that small dog breeds tend to live longer than larger breeds.
Toy and tiny dog breeds become seniors when they reach the age of 10. However, they might age more quickly during their first few years. Medium-sized dogs fit in the middle of the extremes and live up to twelve to fifteen years.
Large dog breeds, on the other hand, age very quickly. They mature more slowly first but nearly reach middle age at 5. For instance, St. Bernards or Great Danes age very quickly and only live to about six or seven years of age.
The cause for a big dog’s short lifespan is still unknown but researchers believed that the presence of large amounts of IGF-1 growth hormone in a large dog breed’s bloodstream pushes them to age swiftly compared to other dog breeds. Further, IGF-1 is also associated with the heightened risk of death due to heart disease, cancer, and other age-related diseases both in humans and animals.
Since the longevity of a dog strongly correlates with its size, remember that you calculate a dog’s age in human years by breed and size. Listed below is a guide to help you identify where your pooch fits in terms of size:
- Small dog breed = 9.5 kg or less
- Medium dog breed = 9.6 kg – 22 kg
- Large dog breed = 23 kg – 40kg
- Giant dog breed = above 41 kg
Steps in calculating a dog’s age in human years
- Determine the size of your pooch.
For an accurate assessment, you can have your dog weighed at the vet instead of at home. Then, use the guide above to check what category he falls into. - Calculate your dog’s age after age 2
Photo Credit: Science Alert
When dogs reach their second year, it is the time where their size starts to affect their age. That’s why you must begin estimating your dog’s age at this point. For each year after your dog has reached his second year, begin adding the number of years to his dog age based on your dog’s weight (Please use the chart above for reference.)
2. Based on the dog’s teeth
For dogs that have been adopted or acquired in their older years, calculating their age can be a bit of a challenge. But by looking at your dog’s teeth, you can get the approximate age in human years.
- 8-weeks-old: Puppy has a complete set of baby teeth.
- 7-weeks-old: The pooch’s adult teeth, which will be shiny and white, are all present
- 1 to 2-years-old: The colour of his teeth will turn into a duller white and the others at the back will be prone to yellowing.
- 3 to 5-years-old: His teeth will be a little worn and have a little amount of tartar build-up.
- 5 to 10-years-old: Your dog will have even more worn teeth with signs of gum diseases.
- 10 to 15-years-old: The teeth will be much worn with significant tartar build-up. Your dog might also lose some teeth due to old age.
