Heavenly Stems & Earthly Branches 干支 Glossary

The ten stems and twelve branches whose combinations make the 60-step cycle behind every pillar, year, month, day and two-hour period in the tradition.

Ganzhi · 干支 · gānzhī · 天干地支 · tiāngān dìzhī · stems and branches · sexagenary cycle

Source credibility (S/A/B/C/X): S    Rule computability (A/B/C): A

What it is

Ten heavenly stems （天干） — 甲乙丙丁戊己庚辛壬癸 — pair with twelve earthly branches （地支） — 子丑寅卯辰巳午未申酉戌亥 — in a fixed alternation producing a 60-step cycle （六十甲子）. The branches also carry the twelve zodiac animals, the twelve two-hour periods, the twelve months of the solar-term year, and the compass sectors used in 24 Mountains (each branch plus its adjacent stem subdivides into three mountains).

Because stems and branches count continuously while calendar labels reset, the cycle is the engine's lingua franca: day pillars are counted, year/month pillars are solved from astronomical boundaries, and everything is cross-checked against continuous-cycle arithmetic.

School differences

None on the cycle itself — the 60-step order is universal. Differences arise only in which boundary event starts a labelled year or month: see the Lichun entry and the School Dispute Register.

How this engine computes it

• The day pillar is a pure continuous count; the year and month pillars are computed from the exact solar-term instants (the month pillar flips at each 節, not at the lunar month start).
• Both conventions are exposed as parameters (year_convention, day_boundary) and returned side by side when they differ.
• Stem/branch names are emitted consistently in Chinese and pinyin-tagged English across web, API and MCP surfaces.

Related entries

Four Pillars (BaZi) · Solar Terms · 24 Mountains · Year Pillar (Lichun boundary)

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