Last updated: October 2026
How old is my dog in human years?
Short answer: forget the 7x myth. The first dog year equals 15 human years, the second adds 9 (total 24), and each year after adds 4 for small dogs, 5 for medium, 6 for large and 7 for giant breeds. Pick your dog's size and age above for the exact number.
Why the 7-year rule is wrong
Dogs mature far faster in their first two years — a 1-year-old dog is developmentally closer to a 15-year-old human than a 7-year-old. And size matters: large breeds age faster per year than small ones, which is why a Great Dane is senior at 6 while a Chihuahua is still middle-aged. In 2019, UC San Diego researchers proposed an epigenetic formula based on DNA methylation — human age = 16 × ln(dog age) + 31 — available above as the "Epigenetic formula" option.
Cat years work the same way
Cats follow the same early curve: year one is 15 human years, year two adds 9, and each year after adds about 4. Switch to the Cat tab above — no size selection needed.
Frequently asked questions
How old is my dog in human years?
It's not simply 7x. The rule vets use: the first dog year equals 15 human years, the second adds 9 (total 24), and each year after adds 4 for small dogs, 5 for medium, 6 for large and 7 for giant breeds. Select your dog's size and age above for the exact number.
Is the 7 years per dog year rule true?
No — it's a myth. Dogs mature much faster in their first two years (a 1-year-old dog is roughly a 15-year-old human, not 7), and large breeds age faster than small ones. A 2019 UC San Diego study proposed an epigenetic formula: human age = 16 × ln(dog age) + 31.
How old is my cat in human years?
The first cat year equals 15 human years, the second adds 9 (total 24), and each year after adds about 4. So a 5-year-old cat is roughly 36 in human years. Switch to the Cat tab above to calculate.
When is a dog considered a senior?
It depends on size: giant breeds around 6, large and medium breeds around 7, small breeds around 8. Cats are generally considered senior at 11. The calculator shows your pet's life stage automatically.
Do small dogs live longer than big dogs?
Yes — small dogs typically live 12-16 years while giant breeds average 8-10. Large dogs age faster per year, which is why the calculator adds more human years per dog year for bigger sizes.