The twelve Earthly Branches (地支, dìzhī) are the lower half of every BaZi pillar — and where the chart's most textured qi lives. Unlike the Heavenly Stems (天干), which carry a single, pure elemental force, each Branch holds hidden stems (藏干): one to three stems buried within it, encoding mixed and sometimes contradictory energies that only surface under the right combinations or luck cycles. The animal name attached to each Branch — Rat, Ox, Tiger, and so on — is a folk mnemonic, not the definition; the Branch itself is a precise intersection of element, polarity, season, and double-hour that no animal image fully captures.
One point of divergence worth knowing: schools disagree on the polarity of 子 (Rat), 午 (Horse), 巳 (Snake), and 亥 (Pig). The sequential school assigns polarity by position in the cycle — 子 as yang, 午 as yin, and so on in strict alternation. The hidden-stem essence school reads polarity from the dominant stem concealed inside the Branch — 子, housing 癸 (yin Water), becomes yin; 午, housing 丁 (yin Fire) alongside 己, similarly shifts. Neither reading is wrong; they are lenses, and a careful practitioner notes which school an author is using before drawing conclusions.
The solar year in BaZi begins at Li Chun (立春, roughly 4 February) — not at the Lunar New Year, not at 1 January. This single fact corrects the single most common error in Branch calculations.
