The solar term system has 12 principal terms to indicate the sun's longitudes at every 30 degrees.
The 1st month that does not have a principal term is determined as the leap month.
This widespread change occurred on October 1, 1949, when Mao Zedong, who led the People's Republic of China, ordered that the year should be in accord with the Gregorian calendar.
According to Helmer Aslaksen, of the National University of Singapore, there are 2 rules of thumb used to calculate the new year in the Chinese calendar.
The 1st rule of thumb is that Chinese New Year should be the new moon closest to the beginning of spring (in the northern hemisphere), known as falls close to halfway between 2 new moons. Chinese New Year will always fall between January 21 and February 21.
A leap year in the Chinese calendar does not necessarily fall at the same time a leap year occurs in the Gregorian calendar.
One must calculate the number of New Moons between the 11th month in 1 year, which is the month with the December solstice, and the 11th month in the following year to figure out if a year is a leap year.
A leap month is added to the Chinese calendar about once every 3 years.
The name of the leap month is the same as the previous lunar month.A similar naming of days and months is no longer used but the date name is still listed in calendars.It has been customary to number the 60-year cycle since 2637 BCE when the calendar was supposedly invented.Another phase was added to the calendar because the system was meant to be for popular use.Twelve animals were associated with each year during the Chou period.However, there have been various folktales linked the origin of the 12 animals.