Dog Years to Human Years: What’s the Latest Math?

The 7:1 ratio is out. There’s new research on how to convert your dog’s age to human years.

Cropped Image Of Dog
Because dogs and humans live so closely, we share many factors that contribute to the aging process. © Alan Price / Eyeem /Getty Images

You’ve heard the old saying — to calculate your dog’s age in human years you multiply his age by seven. A more modern idea accounts for breed size, where small and medium-sized breeds are thought to age at a slower rate than large and giant breed dogs.

All mammals progress through the life stages of embryonic development, birth, infancy, youth, adolescence, adult and senior, but not at the same rates. The new math for determining how old a dog is in human years changes our perception of just how old our dogs are.

The latest research on converting dog years to human years

In a study published by Cell Systems, researchers from the University of California San Diego School of Medicine, along with leading veterinarians, formulated a new way for determining age in dogs that, pending further research, works for multiple dog breeds.

Here’s the theory: Nuclear DNA stays the same over time, while epigenetic modifications enable cells to act differently depending on what tissue and organs they are a part of, or what stage of life the organism is in.

Methyl groups, or small molecules made of one carbon and three hydrogen atoms, attach themselves to segments of nuclear DNA to start or stop DNA activity without changing the structure. They turn them “off” or “on” to change the gene’s actions. By tracking molecular changes, scientists can determine the age of genomes by translating an individual’s methylome to an accurate estimate of age.

Do humans and dogs age in the same way?

Dogs offered a unique opportunity to the researchers. Dogs share many aspects of human life, including factors that contribute to aging, such as diet, environment and chemical exposure. Physiologically, dogs age in much the same way as humans, although quicker. The study used Labradors and compared their methylation changes to humans. It showed a nonlinear relationship that translates dog-to-human years and matches major physiological events between the two species. The predictability of these changes mapped epigenetic clocks that calculated age accurately and shaped the formula.

How do I figure out how old my dog is in human years?

The research shows that a 1-year-old dog is comparable to a 30-year-old person, while a 4-year-old dog is similar to a 52-year-old human. When a dog reaches 7 years old, his aging process slows.

To calculate the specific age of your dog, start with the natural logarithm (ln) of the dog’s age, multiply by 16 and add 31:

  • Human Age = 16(ln of Dog Age) + 31.

A natural logarithm is defined as the amount of time it takes “e” units of growth, where e equals the amount of growth after one unit of time. This shows mathematically growth in babies to adolescence is quick and tapers off to a slower rate in the adult and senior years.

For example, an 8-week-old puppy is approximately 0.15 years old (8 weeks divided by 52 weeks in a year). Take the natural logarithm of 0.15, which is -1.897, and multiply by 16 to get -30.35. Add 31 and your puppy is approximately 0.65 human years old. Multiply 0.65 by 52 weeks to get 33.8 weeks, or 8.45 months. This associates the puppy with an 8-and-a-half-month-old baby, corresponding to the infant stage of development.

Improving your dog’s life expectancy

Although other dog breeds need to be researched to confirm these results apply to all dogs aside from Labradors, this study does shed light on how dogs age, which could improve their lifespan overtime based on decisions we make. Knowing how old your dog is in human years is just one part of providing the best care for your dog.

10 thoughts on “Dog Years to Human Years: What’s the Latest Math?”

  1. I have either spaniels or border collies or a cross of these two breeds (sprollies). I calculate as 20 for first year and 4 years thereafter. So a 16 year old dog would be 80 in human years, an 11 year old 60. It seems to be about right for a large dog.

  2. This makes no sense to me at all.
    I am not understanding the concept.
    How does Human Years: 1 Dog years: 31
    go up 11 years for Human Years: 2 Dog years: 42
    then only goes up 6.2 years for Human Years: 3 Dog years: 48.5
    and so on?

  3. I don't understand how you do the calculations it is confusing how to calculate the (In of Dog Age) using the formula
    Human Age = 16(ln of Dog Age) + 31. My dog is 8 years old I don't understand how to get the (in of Dog Age)?

  4. Dogs don't have an extended childhood like us so, according to this equation the first (human) year of a dog's life is equal to 30. Then they're pretty much middle aged until they are ten, then are just old but their aging slows down to that of humans.

    Human Years: 1 Dog years: 31
    Human Years: 2 Dog years: 42
    Human Years: 3 Dog years: 48.5
    Human Years: 4 Dog years: 53
    Human Years: 5 Dog years: 57
    Human Years: 6 Dog years: 60
    Human Years: 7 Dog years: 62
    Human Years: 8 Dog years: 64
    Human Years: 9 Dog years: 66
    Human Years: 10 Dog years: 68
    Human Years: 11 Dog years: 69
    Human Years: 12 Dog years: 71
    Human Years: 13 Dog years: 72
    Human Years: 14 Dog years: 73
    Human Years: 15 Dog years: 74
    Human Years: 16 Dog years: 75
    Human Years: 17 Dog years: 76
    Human Years: 18 Dog years: 77
    Human Years: 19 Dog years: 78
    Human Years: 20 Dog years: 79

    1. There is a link above to help calculate the natural log. Using this tool to first calculate the natural log of 12.5, then multiplying the result by 16, and adding 31, the age of Bill's dog equals 71 human years. Sorry for the math!

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