CALENDARS & SYMBOLS · 5 MIN READ

The Chinese Sexagenary Cycle (Gan-Zhi)

How the sixty stem-branch pairs mark years, months, days, and double-hours in traditional calendars.

The Chinese sexagenary cycle, also called the stem-branch cycle or Gan-Zhi (干支, gānzhī), is a sixty-step sequence formed by pairing the ten Heavenly Stems (天干, tiāngān) with the twelve Earthly Branches (地支, dìzhī). Its first pair is Jiazi (甲子, jiǎzǐ); the last is Guihai (癸亥, guǐhài). The cycle then begins again.

“Sexagenary” means sixty-part. The sequence is not a list of sixty unrelated labels: each position is produced by advancing both smaller cycles one step at a time. Since ten and twelve share a common factor of two, only compatible stem-branch pairs occur, and the full alignment repeats after sixty steps.

What the cycle records#

Traditional calendars use stem-branch pairs for years, months, days, and double-hours. A date may therefore carry several cyclical labels at once. BaZi (八字, bāzì) uses the year, month, day, and hour pillars to encode a recorded birth time. Other methods use the date or hour as an input to a chart or divination procedure.

The same label can play different roles. A day stem in a BaZi chart is not the same thing as the day's stem considered in a calendar almanac. A branch can indicate a time segment, a position in the sixty-pair cycle, or a traditional animal association. The surrounding method tells you which role is relevant.

Calculating a date is not interpreting a chart#

To calculate a stem-branch label, a practitioner needs a date convention and a reliable calendar conversion. For a birth near midnight, a day-boundary convention matters. For a date near a solar term, the time of the astronomical boundary matters. Historical time zones and daylight-saving changes can also affect a recorded clock time.

Once the label is calculated, interpretation is a separate step. Different schools may assign different roles or weights to the same signs. A reproducible calculation helps other readers check the input; it does not settle which interpretation is correct or prove that it predicts events.

Study exercise#

Write the ten stems and twelve branches in order. Starting from Jiazi, advance both lists together for a few steps. Then compare your result with a calendar and record the date, time zone, and source used. If two tools disagree, check boundary assumptions before treating the difference as an arithmetic error.

The sexagenary cycle article provides a reference overview. See also Heavenly Stems and Earthly Branches, Explained.