According to Purina, there is no scientific way to specifically calculate a cat's age in human years. However, the steps below provide a general comparison.
Purina estimates that a cat's first two years equate roughly to a human's first 25.
A two-year old cat would be 24 in human years.
If a cat is 3 years old, it is 28 in human years. If it is 4 years old, it is 32.