Dog and Cat Age Calculator
Convert your dog's or cat's age into human years, allowing for the fact that pets grow up fast and that bigger dogs age faster.
In human years
39 years old
A 5-year-old medium dog is roughly 39 in human years.
How it's worked out
- First yearabout 15 human years
- Second yearabout 9 more
- Each year afterabout 5 more
- A rough guide: pets mature fast in their first two years, and bigger dogs age faster after that. The old "multiply by 7" rule isn't accurate.
How it's worked out
Year 1 ≈ 15 · Year 2 ≈ +9 · Each year after ≈ +4 (cats, small dogs) to +7 (giant dogs)
Worked example
A 5-year-old medium dog: 15 + 9 + 3 × 5 = 39 in human years.
Questions people ask
How old is my dog in human years?
Roughly 15 human years for the first year, 9 more for the second, then about 4 to 7 a year depending on size. A 5-year-old medium dog is about 39.
Is one dog year really seven human years?
No. That old rule is wrong for young dogs, which mature much faster, and for large breeds, which age faster later on.
How old is my cat in human years?
About 15 at 1 year, 24 at 2, then about 4 more each year. A 10-year-old cat is about 56.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem