Although many people still believe that one dog year equals seven human years, the calculation is a bit more complicated. The comparison between dog and human years depends on the breed and size, and it is not as linear as previously thought.
So, how do dog years work? Keep reading to find out.
Factors Influencing Dog Age
No two dogs age the same, and calculating dogs’ age is much more complex than just multiplying or adding numbers. So, let’s first see which factors are crucial for determining our dog’s age.
Size
In most animal species, bigger size means quicker aging and death, and this also applies to dogs. A study has found that smaller-breed dogs can live up to 5 years longer than giant breeds.
There are more than a few reasons for this. Still, some speculations say that due to their fast growth, there are more possibilities for abnormality and cancer growth.
Obese and overweight pets are also at a higher risk of cancer than those that are fit.
Breed
The same study has found that purebred dogs live slightly shorter than mixed ones. But, the difference is not as significant as with size. Purebred smaller dogs still live longer than mixed-breed large dogs.
Also, separate breeds have different diseases affecting them, so they age differently.
Lifestyle
Similar to how humans can look younger than they are, so can dogs. If they lead a healthy lifestyle, the calculated age will be just a number. Your vet might give your dog a much lower or higher age estimate depending on how well you’ve been taking care of your pet.
Different Approaches to Calculating Dog Years to Human Years
We all know that dogs age faster than humans, but comparing their years to ours is not that easy.
With that in mind, a few methods have explained how dogs age and how to convert their age to human years. Let’s look at them.
1 to 7 Year
A theory that one human year is equal to seven dog years has been popular for years. Even though this makes it easy for pet owners to calculate their pet’s age, it’s simply not accurate.
It originated from the assumption that humans live for 70 years and dogs for 10, on average. However, since there are many factors to dog aging, and their aging is not linear, it won’t give accurate results.
Genome Study
A study on molecular changes in the genome of dogs and humans had some interesting findings. They came to the conclusion that a one-year-old dog is around 30 years old in human age.
They grow steadily until they are seven years old, when their aging starts to slow down.
They created a formula — human_age = 16 ln(dog_age) + 31. There are two downsides to this study, though. First, it’s difficult for an average person to calculate. Second, their study focused only on Labrador Retrievers, and it cannot match the aging of all dogs.
American Veterinary Association Calculation
The American Veterinary Association starts with the presumption that a one-year-old dog is equivalent to a 15-year-old human. A two-year-old dog is nine years older in dog years, meaning it would be equal to a 24-year old human.
If you compare human and dog stages of “maturity,” you’ll see that it’s pretty accurate. Dogs finish changing their baby teeth by the age of 6 months, while humans do so between the ages of 7 and 8.
Dog reproductive ability starts at around 8–9 months, which can be associated with puberty and adolescence in humans, which starts at around 12 years of age.
This is the most used and currently the only approved way of calculating, so we’ll use it too.
How to Compare Human Years to Dog Years?
If you want to know how old your dog is, you can use a calculator — or you can easily calculate it yourself.
Fast Calculation
1-year-old — 15 years
2-year-old — 24 years
After that, you can add five dog years for each human year that passes. Be aware that this is an approximate calculation.
If you want a more exact result, check out our chart.
Dog Years vs. Human Years Chart
| Dog’s True Age | Dog Age in Human Years by Breed Size | |||
| Small | Medium | Large | Giant (100+lbs) | |
| 1 | 15 | 15 | 15 | 12 |
| 2 | 24 | 24 | 24 | 22 |
| 3 | 28 | 28 | 28 | 31 |
| 4 | 32 | 32 | 32 | 38 |
| 5 | 36 | 36 | 36 | 45 |
| 6 | 40 | 42 | 45 | 49 |
| 7 | 44 | 47 | 50 | 56 |
| 8 | 48 | 51 | 55 | 64 |
| 9 | 52 | 56 | 61 | 71 |
| 10 | 56 | 60 | 66 | 79 |
| 11 | 60 | 65 | 72 | 86 |
| 12 | 64 | 69 | 77 | 93 |
| 13 | 68 | 74 | 82 | 100 |
| 14 | 72 | 78 | 88 | 107 |
| 15 | 76 | 83 | 93 | 114 |
| 16 | 80 | 87 | 99 | 121 |
As you can see, smaller dogs age a lot slower than others, while giant breeds age the least during the first two years but speed up later.
This is because smaller breeds grow until the age of 8 months, while giant breeds aren’t fully grown until they’re 18 months old.
Dog Life Stages
If you’d like a more detailed description of dog life stages, here is what you should know. Not every breed goes through the stages at the same time, and size can be crucial for the changes. Look at our table to find out more.
| Dog size | Puppy | Adult | Senior | Geriatric |
| Small
(<20lbs) |
First 8 mo. | 8 mo. to
10–12 yrs. |
10–12 yrs. to 15–16 yrs. | 16 years+ |
| Medium
(21–50lbs) |
First yr. | 1 yr. to
8–9 yrs. |
8–9 yrs. to 12–13 yrs. | 13 years+ |
| Large
(51–100 lbs) |
First 15 mo. | 15 mo. to
6–7 yrs. |
6–7 yrs. to 11–12 yrs. | 12 years+ |
| Giant
(>100 lbs) |
First 18–24 mo. | 18–24 mo. to 6 yrs. | 6 yrs. to 8–9 yrs. | 9 years+ |
FAQ
How to know how old my dog is?
To find out how old your dog is, you start with 15 years for the first year, add 9 for the second, and then add five years for all the next. You can look at our chart for the more exact results.
In the end, you can always consult your vet, and they can determine the age more accurately.
Why do dogs age so fast?
Dogs’ metabolism works much faster, so they age faster than humans do. Their hearts, bones, muscles, and other organs also wear out much faster.
How does a 72-year-old person compare to a dog?
A 72-year-old human is equal to a 14-year-old dog. This is true only for smaller dogs, though — giant breeds turn 72 around the age of 9.
Is 1 human year 7 years for a dog?
No, one human year is not the same as seven dog years. Dogs’ age process is not linear. Depending on the size and current age of the dog, one year can be anywhere between 4 and 15 years in dog age.
What is 1 dog year in human years?
One human year is equal to approximately 15 dog years, so one dog year would be equal to less than a month in human years. But, it’s only an approximation, since dog age is not linear. To understand the difference between human and dog years better, look at our chart.
Final Thoughts
We hope that now you understand just how different human and dog years really are. With the new methods of calculation that are much more accurate than the old 1 for 7, you’ll always be sure how old your dog is.
So, if anyone asks you — how do dog years work? — send them this text, and they’ll be experts in no time.
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