How the pet age calculator works
Veterinary groups including the American Animal Hospital Association and the American Veterinary Medical Association use a stepped scale. A pet's first year equals about 15 human years and the second adds about 9 more. After that each year adds roughly 4 to 7 human years depending on species and size.
Each year after: cats and small dogs +4, medium dogs +5, large +6, giant +7
Large and giant breeds have shorter lifespans and are considered senior at around 6 to 7, while small dogs and cats reach senior status around 10. A 2019 University of California, San Diego study using DNA methylation suggested an even steeper early curve for dogs, but the stepped scale remains the standard used by vets.
Worked example
A 6-year-old medium-sized dog is 24 + 4 × 5 = 44 human years, a mature adult. A 6-year-old Great Dane would be about 52 and already a senior, while a 6-year-old cat is about 40.
Frequently asked questions
Is one dog year really seven human years?
No. Dogs mature much faster in the first two years and then age at a rate that depends on size.
How old is a 10-year-old cat in human years?
About 56, using 15 for the first year, 9 for the second and 4 per year after.
Why do big dogs age faster?
Large breeds grow quickly and have shorter average lifespans, so they reach the senior stage sooner.
When is a dog considered senior?
Roughly at 10 for small dogs, 8 for medium, 7 for large and 6 for giant breeds.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.