Prior to adoption of the Western solar calendar system, China exclusively followed a lunar calendar in determining the times of planting, harvesting, and festival occasions. Though today people in China use the western calendar for most practical matters of daily life, the old system still serves as the basis for determining numerous seasonal holidays. This coexistence of two calendar systems has long been accepted by the people of China.

A lunar month is determined by the period required for the moon to complete its full phasic cycle of 29 and a half days, a standard that makes the lunar year a full 11 days shorter than its solar counterpart. This difference is made up every 19 years by the addition of seven lunar months. The 12 lunar months are further divided into 24 solar divisions distinguished by the four seasons and times of heat and cold, all bearing close relationship to the yearly cycle of agricultural work.

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