How old is your dog in human years? Why the 7-year rule is wrong
Scientists compared aging in dogs and people at the level of DNA and found a better formula than multiplying by 7. Try the calculator and see how your dog compares.
Ask anyone how to convert dog years and you will hear the same answer: multiply by seven. It is easy, and it is wrong. The American Veterinary Medical Association states plainly that, contrary to popular belief, dogs do not age at a rate of 7 human years per dog year.3 Researchers at the University of California San Diego went further and built a formula from the dogs' own DNA.
The science: a clock written in DNA
As people and animals age, small chemical tags called methyl groups attach to their DNA in patterns that change over time. Scientists use those patterns as an "epigenetic clock."2
The team compared these patterns in the blood of 104 Labrador retrievers, from puppies to 16-year-olds, with data from 320 people aged 1 to 103.2 Dogs and humans turned out to follow similar patterns, especially early and late in life, which let the researchers line up the two clocks.2
Their combined function is: human age = 16 × ln(dog age) + 31, where "ln" is the natural logarithm.1 The authors found it agreed well with the times at which dogs and people reach the same milestones, from infancy to late life.1
Try it with your dog
What the formula shows
The curve is steep at first and then flattens. Dogs race through childhood: the National Institute on Aging's summary of the study compares an 8-week-old puppy to a baby of about 9 months.2 After that, each extra year adds less and less.
| Dog's age | About this many human years | "Times 7" rule |
|---|---|---|
| 1 | 31 | 7 |
| 2 | 42 | 14 |
| 4 | 53 | 28 |
| 6 | 60 | 42 |
| 8 | 64 | 56 |
| 10 | 68 | 70 |
| 12 | 71 | 84 |
| 14 | 73 | 98 |
Figures computed with the study's formula and rounded.1 The NIA's own example: a 12-year-old Labrador compares with a person of about 70.2
A Labrador formula, not a law of nature
The study used Labradors, and the NIA notes that the next step is testing the formula on other breeds.2 That matters, because size changes how fast dogs age. The AVMA explains that larger breeds tend to have shorter life spans than smaller ones, and that experts consider a dog senior in the last 25 percent of its breed's expected life span.3 On average, that works out to:3
- small or toy breeds under 20 pounds: 8 to 11 years;
- medium breeds of 20 to 50 pounds: 8 to 10 years;
- large breeds of 50 to 90 pounds: 8 to 9 years;
- giant breeds over 90 pounds: 6 to 7 years.
So treat the calculator as a good estimate for a medium or large dog, and a rough one for a Chihuahua or a Great Dane.
Why the number is worth knowing
Knowing your dog's age in human terms is more than trivia. It helps explain why a 4-year-old dog behaves like a settled adult rather than a teenager, and why an 8-year-old may start to slow down. The AVMA notes that older dogs often need changes in their routine, diet and home, such as more comfortable sleeping areas.3
Wondering about your cat? See our guide to your cat's age in human years, which follows a different curve.
