Choose dog or cat, enter their age, and for dogs pick an adult size. The "7 human years per dog year" rule is a myth: pets age very quickly in their first two years, then more slowly, and big dogs age faster than small ones.
Cats and dogs mature very fast: a one-year-old is roughly like a 15-year-old human, and a two-year-old like a 24-year-old. After that, each pet year counts for fewer human years. For cats, the guidance used by International Cat Care and the American Animal Hospital Association adds about 4 human years per cat year after age two, so a 10-year-old cat is about 56.
Dogs age at different speeds depending on size. After the first two years, this calculator adds about 4 human years per year for small dogs, 5 for medium, 6 for large and 7 for giant breeds. That’s why a 10-year-old Chihuahua is roughly 56 in human terms, while a 10-year-old Great Dane is closer to 80.
For dogs, the page also shows a DNA-based formula from a 2019 University of California San Diego study of Labrador retrievers, which compared changes in DNA methylation: human age ≈ 16 × ln(dog age) + 31. It suggests puppies age even faster early on, but it was based on one breed, so treat it as a second opinion rather than the answer.
No. That old rule of thumb is too slow for young dogs and too fast for older small dogs. A one-year-old dog is closer to 15 in human terms, and a dog’s ageing rate afterwards depends on its size.
Large and giant breeds have shorter lifespans and reach “senior” sooner, often around 6–7 years, while many small breeds live into their mid-to-late teens. Researchers are still studying why growth rate and size affect ageing.
About 15 at one year, 24 at two, then add roughly 4 years for each year after that. A 12-year-old cat is about 64 in human years.
Cats are usually considered senior from around 11 years and “super senior” from 15. Dogs vary by size: giant breeds can be senior at about 6, large dogs at around 7–8, and small dogs closer to 10.
A 2019 UC San Diego study matched changes in DNA methylation in Labradors to humans and proposed human age = 16 × ln(dog age) + 31. It fits the rapid ageing of puppies well but was only tested on one breed.
