Dog Age Calculator
Find your dog’s age in human years, adjusted for its size.
About this tool
Uses the common veterinary guideline: the first year equals about 15 human years, the second about 9 more, then 4 to 7 years for each year after, depending on size. Also shows the 2019 DNA-methylation formula (16 × ln(age) + 31). Both are estimates.
The old rule that one dog year equals seven human years is too simple: dogs grow up very quickly in their first two years, and large breeds age faster than small ones after that. Enter your dog’s age and size to get an estimate in human years using the guideline vets commonly use, alongside a newer estimate based on changes in dogs’ DNA, and see which life stage your dog is in.
How to use the Dog Age Calculator
- Enter your dog’s age in years; use decimals for months, such as 1.5.
- Choose its fully grown size.
- Read its age in human years and its life stage.
- Compare with the DNA-based estimate, which does not depend on size.
A 5-year-old medium dog
The first year counts as 15 human years and the second as 9 more, making 24. Each of the next three years adds about 5 for a medium dog, so a 5-year-old is about 24 + 3 × 5 = 39 in human years, an adult. A giant breed of the same age would be about 45. The DNA formula gives 16 × ln(5) + 31, about 57.
Why there is no single answer
Dogs reach adulthood within about two years, which is why the first years count for so much. After that, size matters: small breeds often live 14 to 16 years or more, while giant breeds may live 8 to 10, so a large dog of the same age is older in biological terms. The vet guideline reflects this with more human years per year for bigger dogs. In 2019, researchers at the University of California San Diego compared age-related chemical changes in dog and human DNA and proposed human age = 16 × ln(dog age) + 31, which ages young dogs especially fast; it was based mainly on Labradors. Treat both as rough guides, and look at your dog’s health and energy rather than any single number.
Frequently asked questions
Is one dog year really seven human years?
No. That rule is a rough average. Dogs age much faster in their first two years and more slowly after that, depending on size.
When is a dog considered senior?
Roughly from 7 years for large and giant breeds and from about 10 years for small breeds.
Why do big dogs age faster?
Larger breeds grow quickly and tend to have shorter lifespans, though the exact reasons are still being studied.
Does this work for cats?
No. Cats age differently; a cat age calculator uses its own scale.