Dog Age Calculator
Updated October 2026
Enter your dog\u2019s age and adult size to convert dog years to human years — with the size-adjusted rule veterinarians commonly cite.
How the conversion works
The old “seven dog years per human year” rule is wrong — dogs age much faster in their first two years than later. The calculator uses the commonly cited veterinary rule: the first year counts as 15 human years, the second year adds 9, and each year after that adds a size-dependent amount.
Size matters because large and giant breeds age faster than small ones. After year two, each additional year counts as about 4 human years for toy and small dogs, 5 for medium dogs, 6 for large dogs, and 7 for giant dogs.
Why it is only an estimate
Real aging depends on breed, genetics, weight, and health — two 8-year-old dogs can be in very different shape. Researchers have even proposed epigenetic clocks that measure aging from DNA methylation, but for everyday intuition the size-based rule is close enough.
Use the result to calibrate expectations: a 7-year-old Great Dane is well into senior territory, while a 7-year-old Chihuahua is solidly middle-aged.
Frequently asked questions
Is the 7 dog years rule accurate?
No. Dogs age fastest in their first two years — a 1-year-old dog is roughly a human teenager, not a 7-year-old child. The 7x rule underestimates young dogs and overestimates old ones.
Do small dogs live longer than large dogs?
On average, yes. Small breeds often live 12–16 years while giant breeds average 8–10. That is why the calculator adds fewer human years per dog year for small dogs after age two.
When is a dog considered a senior?
Roughly speaking: small breeds around 10–12 years, medium breeds around 8–10, large breeds around 7–8, and giant breeds as early as 6. Your vet may start senior screenings earlier based on the individual dog.
How old is my puppy in human years?
A 6-month-old puppy is roughly equivalent to a human child of about 10, and a 1-year-old dog to a teenager of about 15. Puppies mature far faster than the 7x rule suggests.