How is the animal year calculated?

The animal year algorithm is as follows

According to the year (animal year): 12 years old, 24 years old, 36 years old, 48 years old, 60 years old, 72 years old, and each additional 12 years old is your own animal year.

According to nominal age (animal year): 13 years old, 25 years old, 37 years old, 49 years old, 6 1 year old and 73 years old are also 12 years old, but the bases are different.