Instructions
Determine how many calendar years your cat has been alive.
Start with 15 human years for your cat's first year. This calculation is based on the comparative ages when cats and humans reach maturity. Cats reach sexual maturity around the end of their first year, compared to humans, who reach it in their mid-teens.
Allow nine more years for the second year of your cat's life. These numbers are just approximations and may depend on the breed of cat. For example, the Maine Coon does not reach maturity until three to five years of age.
Include four years for each of your cat's subsequent years. There is still a fast rate of development compared to humans but less so than in the first two years.
Add all of these numbers together to determine your cat's age in human years.
Refer to the following chart of cat's ages and their relative human equivalent: 1=15, 2=24, 3=28, 4=32, 5=36, 6=40, 7=44, 8=48, 9=52, 10=56, 11=60, 12=64, 13=68, 14=72, and 15=76.
Consult an online calculator for simplicity or to specify the exact number of years and months of your cat's life (see Resources).
How to Calculate a Cat's Age in Human Years
It has been said that cats age the equivalent of seven human years for each year of life, but in actuality, their rate of development is more variable than that. They have very short infancies and childhoods compared to humans, and then their growth slows down to a more constant rate.