A handy short cut is to remember that the first dog year counts for 31 human years. Then, every time the dog’s chronological age doubles after that, the number of equivalent human years increases by 11. So eight calendar years represents three “doublings” (from one to two, two to four and then four to eight) giving a dog age equivalent of 64 (that’s 31 + 3×11).
A more sophisticated refinement to the factor-of-seven rules has suggested that each of the dog’s first two years correspond to 12 human years while all subsequent years count for four human equivalents. The blue curve in the above figure, which represents this ad hoc rule, shows better agreement with the new logarithmic law.
The underlying assumption is that each calendar year a dog lives though is equivalent to seven human years at any stage of a dog’s life. But new research suggests that things aren’t so simple. And if we look at some basic developmental milestones, it’s clear why.
For example, if you’ve spent a lot of time eating junk food and smoking cigarettes instead of taking exercise and eating healthily, the chances are your biological age will exceed your chronological age. Or, you might be a 60-year-old with the body of a 40-year-old if you’ve looked after yourself well.
Here “ln” represents a mathematical function known as the natural logarithm. The logarithm function is well-known in the non-linear scales for energy released during earthquakes (Richter) or for measuring sound (decibels). It comes in useful for measuring quantities whose sizes vary over many orders of magnitude. It’s even possible, as I explore in my new book The Maths of Life and Death, that a logarithmic experience of the passing of time might explain why we perceive time speeding up as we get older.
What Are Dog Years? Does One Dog Year Equal Seven Human Years?
Multiplying your dog’s age by seven may be easy to do, but it won’t accurately convert dog years to human years.
That’s because dogs mature more quickly than humans do in their early years. In fact, the first year of a dog’s life is equivalent to the first 12-15 of a human’s! The second year of a dog’s life equals about 9-10 human years, while each year after that is worth about 4-5 human years.
So 1 year in dog years could equal anywhere from 4 to 15 human years, depending on which life stage your dog is in, as well as their size.
Additionally, smaller breeds tend to have longer life spans than larger breeds. Smaller dogs are usually considered senior at the age of 7, while large breed dogs might be considered seniors at ages 5 or 6.
How do I calculate my dog’s age in human years?
If you’re looking to calculate your dog’s age in human years more accurately, 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 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, this 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.
For an easier (and also accurate) way to estimate your dog’s age, you can follow this methodology for small, medium, and large dogs under 100 lbs.
So, why is this more accurate than the “one dog year equals seven human years” method?
Because it takes into account that not all dogs breeds age the same way. In general, smaller dogs live longer than larger 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’s 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 dogs (20 to 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:
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 age six. 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.
The Truth About Dog Years (Your Pupper Is Older Than You Think!)
Is one human year equal to seven “dog years” when it comes to a dog’s age? Recent studies have shown that this isn’t exactly true.
We all want our dogs to live forever, and we want to know how our dog’s age relates to human years. So what are dog years, and how do you calculate dog years in human terms?
Here’s everything you need to know to convert dog years to human years—and to understand the science behind it.