The old “one dog year equals seven human years” rule is wrong: dogs grow up much faster in their first two years, and big dogs age faster than small ones after that. Enter your dog’s age and size to get a size-adjusted estimate.
Dog Age Calculator
Your dog’s age in human years, adjusted for size.
How dog years are calculated
A dog’s first year is roughly equal to 15 human years, because a one-year-old dog is already physically mature. The second year adds about nine more (around 24 in total). After that, each year counts as roughly 4 to 7 human years depending on size: small dogs age the slowest and giant breeds the fastest.
For comparison, the calculator also shows the formula from a 2020 University of California San Diego study that measured DNA changes (an “epigenetic clock”) in Labrador Retrievers: human age ≈ 16 × ln(dog age) + 31. It makes young dogs look “older” than the traditional chart does.
Why size matters
Large and giant breeds reach old age sooner. A Great Dane may be a senior at 6 or 7, while a Chihuahua can stay middle-aged well past 10. That is why vets usually start senior check-ups earlier for bigger dogs.
Frequently asked questions
Is one dog year really seven human years?
No. That rule of thumb ignores how fast puppies mature. A one-year-old dog is closer to a 15-year-old human, and the pace after age two depends on the dog’s size.
How old is a 10-year-old dog in human years?
Roughly 56 for a small dog, 64 for a medium dog, 72 for a large dog and 80 for a giant breed, using the size-adjusted rule of thumb.
When is a dog considered a senior?
Usually in the last quarter of its expected lifespan — around 7–8 for many large breeds and 10–12 for small ones. Ask your vet when to start senior screening for your dog.