Why the 7-year rule is wrong
Dogs don't age at a steady rate. They grow up fast: by their first birthday most dogs are about as mature as a 15-year-old human, and by two they're roughly 24. After that, aging slows to about 4 to 7 human years per dog year, depending on size. Bigger dogs age faster, which is why a Great Dane is a senior at 6 while a Chihuahua might still be middle-aged at 9.
This calculator shows two estimates. The vet chart is the size-based chart used by the American Kennel Club and the American Veterinary Medical Association. The DNA formula comes from a 2020 UC San Diego study that compared age-related DNA changes in Labradors and people: human age = 16 × ln(dog age) + 31.
Common questions
Is one dog year really seven human years?
No. The 7-year rule is a myth. Dogs age much faster early on: a dog's first year is roughly 15 human years and the second adds about 9 more. After that, each year adds about 4 to 7 human years depending on size, with larger breeds aging faster.
How old is a 1-year-old dog in human years?
A 1-year-old dog is about 15 in human years, roughly a teenager. By age 2 most dogs are about 24 in human years.
Why do big dogs age faster than small dogs?
Researchers aren't fully sure, but large breeds grow very quickly and appear to develop age-related diseases earlier. A Great Dane is considered senior at around 6, while a Chihuahua may not be senior until 10 or later.
When is a dog considered a senior?
As a rough guide, small dogs are seniors at about 10 to 12 years, medium dogs at about 8 to 10, and large and giant breeds at about 6 to 8. Many vets recommend twice-yearly checkups once a dog reaches senior age.
What is the new dog age formula?
A 2020 study from UC San Diego compared DNA changes in dogs and humans and proposed human age = 16 × ln(dog age) + 31, where ln is the natural logarithm. It was based on Labrador Retrievers, so it works best for medium to large dogs and isn't meant for puppies under about 1 year.
Sources
Results are estimates for fun and general information. Your vet is the best guide to your dog's health.