About this tool
This calculator converts a dog's or cat's age in years into an approximate human age.
It uses the widely quoted rule of thumb: the first year of a pet's life counts as about 15 human years, the second year adds about 9 more (so 24 at age two), and each following year adds a fixed amount that depends on the animal.
For cats that is about 4 years per year. For dogs it is about 4 for small breeds, 5 for medium breeds and 6 for large breeds, because larger dogs tend to age faster.
For example, a 5-year-old small dog works out to 24 plus 3 times 4, or 36 human years, while a 5-year-old large dog is 24 plus 3 times 6, or 42. A 5-year-old cat is 24 plus 3 times 4, or 36.
The tool also shows a formula proposed in a 2020 DNA methylation study of Labrador retrievers, 16 times the natural logarithm of the age plus 31.
It was derived from one breed, may not fit other dogs or cats, gives much higher numbers than the rule of thumb above, and is shown only for comparison. All of these numbers are approximations.
This page is for reference only and does not replace advice from a veterinarian. Everything is calculated in your browser and nothing is sent to a server.
ⓘ Real ageing depends on breed, genetics, diet, weight and health, and the figures here are not a veterinary diagnosis.
How to use
- Enter your pet's age in years (use decimals such as 1.5 for a year and a half).
- Read the human-age estimates for small, medium and large dogs and for cats.
- Compare with the research formula as a second reference.
- For health questions, ask your veterinarian.