A person's Chinese zodiac sign is determined by locating his year of birth on a Chinese zodiac table, such as the one found on Whats-Your-Sign.com. The Chinese zodiac operates on a 12-year cycle using the Chinese calendar.
The zodiac's rejection of the Gregorian calendar means that people born in January and occasionally February have to pay attention to what part of the Chinese year they were born in. For example, the Chinese New Year in 1984 fell on February 2. Therefore, a person born on February 1, 1984, is represented by the pig, while a person born on February 3 of the same year is represented by the rat.