General concepts

Heavenly Stems and Earthly Branches

Also known as: heavenly stemsearthly branchestian gandi zhi天干地支干支gan zhiganzhisexagenary cyclesixty jiazijia zi cycleten stemstwelve brancheshidden stemscang gan藏干

The ten Heavenly Stems (Tian Gan, 天干) and the twelve Earthly Branches (Di Zhi, 地支) are the two sets of signs of the traditional Chinese calendar. Paired into a cycle of sixty, they name years, months, days and hours and make up the eight characters of a BaZi chart.

Stems and branches are among the oldest signs of Chinese culture. Oracle bones of the Shang dynasty, more than three thousand years old, already count days with them, and from the Han dynasty onwards they also name the years. The paired signs are called ganzhi, and the cycle of sixty they form is still printed in Chinese almanacs.

The ten Heavenly Stems are the five phases, each in a yang and a yin form: Jia and Yi are Wood, Bing and Ding Fire, Wu and Ji Earth, Geng and Xin Metal, Ren and Gui Water. In each pair the first stem is yang and the second yin. The stems are read as the visible, outward side of a pillar.

The twelve Earthly Branches carry the animals of the Chinese zodiac. Zi is the Rat (Water), Chou the Ox (Earth), Yin the Tiger (Wood), Mao the Rabbit (Wood), Chen the Dragon (Earth), Si the Snake (Fire), Wu the Horse (Fire), Wei the Goat (Earth), Shen the Monkey (Metal), You the Rooster (Metal), Xu the Dog (Earth) and Hai the Pig (Water). Each branch also marks a month and a two-hour period of the day: the Zi hour runs from 23:00 to 1:00, the Chou hour from 1:00 to 3:00 and so on round the clock. The year starts with the Tiger month at Li Chun, the four Earth branches stand at the turns of the seasons, and the Zi month contains the winter solstice.

Stems and branches are paired in order, yang with yang and yin with yin. Ten stems and twelve branches meet again after sixty steps, so the cycle runs from Jia Zi to Gui Hai and then begins again. The year 2024 was Jia Chen, Yang Wood over the Dragon, and the next Jia Zi year will be 2044.

A branch is more than one phase. Each holds one to three hidden stems, called Cang Gan (藏干): a main stem and sometimes a middle and a residual one. Zi holds Gui; Chou holds Ji, Gui and Xin; Yin holds Jia, Bing and Wu; Mao holds Yi; Chen holds Wu, Yi and Gui; Si holds Bing, Wu and Geng; Wu holds Ding and Ji; Wei holds Ji, Ding and Yi; Shen holds Geng, Ren and Wu; You holds Xin; Xu holds Wu, Xin and Ding; Hai holds Ren and Jia. The hidden stems explain why a chart can contain a phase that no visible sign shows, and the tradition gives each of them a Ten God like any visible stem. Published tables vary in some details.

Stems and branches also relate to one another. Five pairs of stems combine: Jia with Ji, Yi with Geng, Bing with Xin, Ding with Ren and Wu with Gui. Among the branches the tradition knows six harmonies, six clashes between opposite branches such as Zi and Wu, three harmonies such as Shen, Zi and Chen for Water, and seasonal meetings such as Yin, Mao and Chen for Wood. Whether a combination actually transforms a phase depends on conditions that schools judge differently.

The free BaZi calculator in AstroSensus shows the hidden stems under each branch with their Ten Gods and marks the basic combinations and clashes as present, without claiming that a phase is transformed.