Updated - Apr 4th, 2023
- The well-known one dog year equals seven human years isn’t accurate.
- Researchers have developed a more precise formula to find out how old your dog is in human years. You multiply the natural logarithm of the dog’s age by 16 and add 31.
- A dog’s “human age” is also affected by their breed and size.
It’s common knowledge that one year of a dog’s life is equal to seven human years…or is it? If this is the way you’ve been calculating your dog’s age, don’t worry – you’re not alone. However, the truth is that this method isn’t entirely accurate.
Historically, it’s very likely that the “one dog year equals seven human years” method was created to simply show that dogs age faster than humans. Today, scientists and researchers have developed a more precise method of calculating a dog’s age to human years.
Let’s dig in…
How do I calculate my dog’s age in human years?
So, if you’re asking – “How old is my dog in human years?” – you can use a new formula created by researchers at the University of California San Diego School of Medicine.
These researchers studied the way human and dog DNA changes over time by looking at patterns called methyl groups in humans and Labrador Retrievers. From this research, they concluded that you can calculate a dog’s age to human years by multiplying the natural logarithm of the dog’s age by 16 and adding 31.
Their formula looks like this: (human_age = 16ln(dog_age) + 31). As you can see, the formula is pretty complex, so it can be useful to plug in your dog’s age to an automatic calculator programmed with this formula, like the one here.
Another way to estimate your dog’s age is by following this methodology from the American Veterinary Medical Association (AVMA) for small, medium, and large dogs under 100 lbs:
- The first year of a dog’s life is equal to 15 human years.
- The second year of a dog’s life is equal to about nine human years.
- Each additional year is equal to about four or five human years.
This methodology takes into account that not all dog breeds age the same way. In general, larger dogs tend to have shorter lifespans than smaller dogs, so while a seven-year-old Great Dane might be considered a senior dog, the same isn’t necessarily true for a seven-year-old Chihuahua.
Therefore, it can also be helpful to break down a dog age chart in terms of size, as you’ll see below. Generally, you can group dogs into small dogs (under 20 lbs), medium-sized dogs (20-50 lbs), large dogs (50-100 lbs), and giant dogs (100+ lbs).
Check out the dog age to human age chart below to calculate your dog’s age in human years based on their size group:
Dog Age Calculator Chart
How do dogs age?
As you can see in our dog age chart – aside from the giant category – small, medium, and large dogs age pretty similarly until they reach about six years of age. Then, larger dogs age much faster in comparison to their smaller and medium counterparts. By seven years old, a small dog, like a Dachshund, will be six human years younger than a large breed, like an Airedale Terrier. Why is this?
Ultimately, scientists aren’t completely sure why smaller dogs age slower and live longer than larger ones. According to the American Kennel Club, some researchers hypothesize that it’s because larger dogs are affected by age-related diseases more quickly.
Similarly, larger dogs progress from puppyhood to adulthood much faster, making abnormal cell growth, cancer, and other diseases more likely. It’s for this reason that using the “one dog year equals seven human years” calculation isn’t completely accurate.
While the newer method we’ve shared is more accurate, it’s still difficult to place a general formula on the way dogs age – as this progression will not only depend on your dog’s size, but their breed and individual genetics as well.
What are common signs of aging in dogs?
It can be helpful to look at physical and behavioral clues to determine the age of your canine companion. For example, your dog’s teeth can be a particularly useful indicator of age. According to the Humane Society of the United States, by seven months, all of your dog’s permanent teeth are in; by 1-2 years, they’ll be duller and might have some yellowing; and by 5-10 years, they’ll show wear and possibly signs of disease.
Other indicators of your dog’s age, especially as they reach the senior stage, include:
- Graying hair
- Poor eyesight, cloudy eyes
- Trouble hearing
- Stiff muscles and joints, arthritis
- Lower activity level
- Behavioral changes such as increased anxiety, confusion, accidents in the house, irritability, etc.
Of course, you can always turn to your veterinarian for an accurate estimate of your dog’s age if you’re unsure. Your veterinarian will consider factors, including teeth, body shape, hair or fur, eyes, etc. to give the best estimate of their age.
Why is understanding my dog’s age important?
Using a dog age chart to estimate your dog’s age in human years is a fun and insightful way to learn more about them! It’s important for other reasons, too. Namely, understanding how old your dog is and how they’re aging allows you to properly care for them.
Keep in mind, if you have a larger dog, you’ll want to start looking for signs of aging around five or six, whereas smaller dog owners might not see any real signs until their dog is seven or eight. In any case, once your dog reaches their senior years, you’ll want to keep an extra close eye on their behavior, activity level, and eating habits.
In general, a healthy diet and weight, consistent mental stimulation and physical activity, and regular check-ups at the vet will all help improve your dog’s quality of life.
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The bottom line
At the end of the day, even though the common “one dog year equals seven human years” method has been around for years, it’s not very accurate. Luckily, with new research, we have a better way of estimating the age of our dogs.
Although the math can be a little more complex than a straightforward 1:7 ratio, you can always refer to our dog years to human years chart (or even print it out!) to quickly and easily calculate how old your pup is.