Why are dog years 7 to our 1

One Human Year Does Not Equal Seven Dog Years

No one knows where the dog years rule came from, though virtually all dog owners know it. According to that popular myth, every year a dog spends on the planet is equivalent to seven years for a human. So if a dog lives to be 15years old, she's actually 105 in human years. No one knows where this piece ofcommon knowledge came from, Priceonomics writes,though there are some indications that monks atWestminster Abbey in the 13th century were the first to put forth a similar figure (9:1, in that case).

The problem with this simple ratio is that it's not reflective of reality. As Priceonomics writes, "if this ratio had any truth to it, humans would be capable of reproducing by age seven, and high percentages of us would live to be 150."

Researchers and others who have simply taken the time tothink about the ratio have recognized its illogic for decades. In 1953, for example, a French researcher published a more nuanced version of the rule, based on emperical evidence: dogs age 15 to 20 times faster than humans do during their first year of life, but that ratio soon tapers off to about one dog year being the equivalent of five human years, Priceonomics writes.

Things quickly got more complicated than that, however. As most dog owners know, dog life spans are not equivalent. Larger breeds tend to pass away well before smaller ones. As aging researchers calculated, aten-year-old small dog is about 56 in equivalent human years, for example, whereas a large dog is 66and a super-big dog is 78. To further complicate things, Preceonomics points out, some breeds, like beagles, demonstrate different aging ratios than their equivalent-sized counterparts of different breeds.

So the take home is pretty clear: the 7:1 ratio is a gross oversimplification of how dogs age. But it will probably bedog'syearsbefore that popular myth goes away.

Get the latest stories in your inbox every weekday.

No, a 'dog year' isn't equivalent to 7 human years

Dogs age at different rates compared to humans, but the simple rule of 7 dog years to 1 human year is far from accurate.

If humans aged seven times slower than dogs, then many of us would be able to reproduce at age 7 and live to be 150. Obviously that's not the case.

The reason that dogs can reach full sexual maturity after only a year is that our canine friends age faster during the first two years of their lives than humans do.

Even this general statement is slightly off since smaller breeds tend to mature faster than larger breeds.

Compared to humans, dogs age more quickly at the beginning of their lives and slower toward the end. Therefore, calculating your dog's age relative to yours is a bit tricky, but luckily it's possible.

Since smaller breeds tend to live longer than larger breeds, it's important to calculate your dog's age according to the right category: small (20 pounds or less), medium (21-50 pounds), large (51-90 pounds), or giant (over 90 pounds).

The data in this chart was gathered from Priceonomics.

Although the origins of the seven-year myth is unknown, people have been trying to find a good way to calculate dog years in human years since the 1200s. One of the earliest examples of this is an inscription at Westminster Abbey that dates to the year 1268 and calculates that one human year is equivalent to nine dog years, which was part of some strange way to calculate the end of the world in the 1200s.

The seven-year rule is thought to much more recent. A veterinarian at Kansas State University told The Wall Street Journal: "My guess is it was a marketing ploy. It was a way to encourage owners to bring in their pets at least once a year."

We originally learned about the information in this post through an article in Pricenomics.

How old is your dog in human years? New method better than 'multiply by 7'

How old is your tail-wagging bundle of joy in human years? According to the well-known "rule of paw," one dog year is the equivalent of 7 years. Now, in a study published July 2, in the journal Cell Systems, scientists say it's wrong. Dogs are much older than we think, and researchers devised a more accurate formula to calculate a dog's age based on the chemical changes in the DNA as organisms grow old.

Dogs share the same environment as their owners and receive almost the same standard of health care as humans, providing a unique opportunity for scientists to understand aging across species. Like humans, dogs follow similar developmental trajectories that lead them to grey and become more susceptible to age-related diseases over time. However, how they age on a molecular level is more complicated -- aging rapidly at first and slowing down later in life.

"In terms of how physiologically mature a 1-year-old dog is, a 9-month-old dog can have puppies. Right away, you know that if you do the math, you don't just times seven," says senior author Trey Ideker (@TreyIdeker) of the University of California, San Diego. "What's surprising is exactly how old that one-year-old dog is -- it's like a 30-year old human."

Human and dog DNA, which codes who we are, doesn't change much throughout the course of life, but chemical marks on the DNA, called methylation marks, do. Ideker considers these marks like wrinkles in the genome. "I tend to think of it very much like when you look at someone's face and guess their age based on their wrinkles, gray hair, and other features," he says. "These are just similar kinds of features on the molecular level."

The researchers studied 104 Labrador retrievers spanning from few-week-old puppies to 16-year-old dogs with the help of two canine experts, Danika Bannasch of the University of California, Davis, and Elaine Ostrander of the National Institutes of Health. They compared the changes in the methylation pattern to humans.

The comparison revealed a new formula that better matches the canine-human life stages: human age = 16 ln(dog age) + 31. Based on the new function, an 8-week-old dog is approximately the age of a 9-month-old baby, both being in the infant stage where puppies and babies develop teeth. The average 12-year lifespan of Labrador retrievers also corresponds to the worldwide life expectancy of humans, 70 years.

"I like to take my dogs on runs, and so I'm a little bit more sympathetic to the 6-year-old now," says Ideker, who realized that his dog is pushing 60 according to the new calculation.

In both species, they found that the age-driven methylation largely happens in developmental genes that are hotly fired up to create body plans in utero and regulating childhood development. By the time one becomes an adult and stops growing, "you've largely shut off these genes, but they're still smoldering," says Ideker. "If you look at the methylation marks on those developmental genes, they're still changing."

Focusing on the smoldering developmental genes, the team developed a clock that can measure age and physiological states across different species, while other methylation-quantifying age-predicting methods only do well in one species. Ideker also noted that future investigation in different dog breeds with various lifespans could provide more insight into the new clock. The clock may not only serve as a tool to understand cross-species aging but also apply as clinical practice for veterinarians to take proactive steps to treat animals.

Dog Years Calculator

Quick navigation:

1. Using the dog years calculator
2. How do dog years work?
3. Dog years to human years formula
4. Dog age chart
5. Limitations of the dog age calculator
6. The myth of multiplying dog age by seven to get the human age
7. How many dog years are in a human year?

Using the dog years calculator

This dog age calculator makes it easy to answer the question how old is my dog in human years? If you know your dog's age, just enter it as either a number of years or months. If you don't know the age, but know the dog's birth date, enter it instead and our tool will calculate the dog age in calendar years for you. Finally click "Calculate Human Years".

The output of the calculator is the number of human years, and the equivalent human age in years and months. The tool converts dog years in human years using the formula below.

How do dog years work?

The idea of 'dog years' and 'human years' is to more easily assess what stage of life your dog is: puppy, junior, adult, mature, senior, or geriatric. While different animal associations and veterinary associations might have charts and guidelines for that, for regular people it is much easier to understand when the dog's age is converted to the age of a human in an equivalent phase of physical development. For example, 9 years in dog years are equal to 66 human years, meaning that a 9-year old dog is roughly equivalent to a 66-year old person. Some use the term 'dog years' to mean 'human age equivalent years' while the scientific literature prefers the term 'human years' as more accurate.

The application of this idea is mainly in veterinary work, but it can also help dog owners appreciate the stage of life their pet is in, the physical difficulties that may entail, and so on. Both human and animal life spans have increased over time due to superior care and the availability of more economic resources which can be dedicated to animal healthcare. Continued improvements are unlikely with the current state of medical science, but should they become a reality, we would need to change the way we convert dog years to human years.

Dog years to human years formula

The dog age to human age conversion formula we use in this dog years calculator is based on research by Wang et al. (2020) ^[1]. Its derivation comes from the comparison of human DNA methylation changes with those of dogs. Methylation is experienced by mammalian genomes as they age and can serve as a sort of epigenetic clock. It is linked with life spans of various species and hence can serve as a model of aging.

In the equation above, HumanAge is the age equivalent of a human in years whereas DogAge is the age of the dog measured in calendar years. ln is the natural logarithm function. For example, a 12 year old dog will be nearly 71 in human years.

Dog age chart

The dog years chart below presents the equivalent human age for a given dog age. Since it was calculated using this dog years to human years calculator, it is subject to the same limitations as the tool itself.

The chart can be used to tell how old is 4 in dog years, or the reverse, e.g. what is 9 years in dog years.

Limitations of the dog age calculator

Since the research used to construct this tool was carried on 104 Labrador retrievers spanning a 16-year age range, it may have lower validity for other dog breeds. It should be used with caution for breeds that exhibit a typical lifespan much different than that of Labrador retrievers. E.g. it might work well for a Boxer, a Pitbull or a German Shepherd, but it will probably slightly overestimate the human equivalent age of a Yorkie, a Labradoodle, a Maltipoo, a Cockapoo, a Shetland sheepdog, or a Jack Russell.

Additionally, the dog years equation does not support dog age less than approximately 1.8 months. For this reason a dog age below 1.8 months is calculated as 0.3 human years, which should serve as a rough approximation.

The myth of multiplying dog age by seven to get the human age

For many years the standard advice was that in order to get the human years equivalent, one needs to simply multiply the dog age by seven. So a two year old dog would have a human age equivalent to a 14-yeard old adolescent. However, this advice was never scientifically backed. For example, most dogs would reach sexual maturity between six and twelve months old, well before the two-year mark suggested by this simple approach.

Some believe that this basic advice was given to dog owners so they would remember they need to bring in their companions for a regular check up at the veterinarian office at least one a year. If one dog year is equal to seven human years, that actually sounds like conservative advice.

How many dog years are in a human year?

Understanding the non-linear monotonic relationship between dog years and human years means asking questions like how many dog years are in a human year is meaningless. There is no single number which answers that question. To answer it, one needs to present the functional relationship across the entire life spans of both dogs and humans, just like in the dog age chart.

References

1 Wang T. et al. (2020) "Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome", Cell Systems, DOI: 10.1016/j.cels.2020.06.006