Earthly Branches and Bazi Months (地支與月份)
Learn the Yin-to-Chou month sequence, resolve month branches at solar-term boundaries, and avoid confusing Bazi months with lunar or Gregorian months.
Overview
Bazi month branches run Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai, Zi, and Chou. Each month begins at a major solar-term boundary used by the selected calendar method, not automatically on the first day of a Gregorian or lunar month. Births near a boundary require precise time, location, time-zone history, and an auditable ephemeris.
At a glance
- First branch month
- Yin begins at the Start of Spring boundary
- Spring
- Yin, Mao, Chen
- Summer
- Si, Wu, Wei
- Autumn
- Shen, You, Xu
- Winter
- Hai, Zi, Chou
- Not equivalent
- Branch month is not a Gregorian or lunar-month number
Use the Yin-to-Chou solar-month sequence
The Bazi year’s branch-month cycle begins with Yin and proceeds one branch at a time until Chou.
The apparent mismatch with the Zi-first branch list is expected: canonical branch order and month-year starting convention are separate fields.
- Preserve both sequences explicitly.
- Do not relabel Yin as branch number one.
Resolve the exact solar-term boundary
A month branch changes at the relevant solar term according to the calendar engine and time standard in use.
Near-boundary charts require the actual timestamp, birth location, historical civil offset, and documented astronomical calculation rather than a date-only lookup.
- Use an auditable ephemeris.
- Flag boundary uncertainty instead of guessing.
Month branch carries seasonal command and context
The month branch sets the primary seasonal environment used in many strength and structure methods.
Its hidden stems, relation to the Day Stem, and interactions with the other three branches still need separate evaluation.
- Keep month command visible.
- Do not let one month label erase the chart.
Do not mix lunar, solar, and civil calendars
Lunar New Year, the first day of a Gregorian month, and a Bazi solar-month boundary are different events and can produce different labels.
Calendar conversion errors can change the entire month pillar, so uncertain inputs should not support medical, legal, financial, or relationship predictions.
- Name the calendar convention.
- Recalculate when time or location changes.
Sources and editorial basis
- Hong Kong Observatory: Heavenly Stems and Earthly Branches香港天文台「天干地支」：十二地支可配十二個月份，與通俗生肖用途分開An official modern reference for the canonical stem and branch orders, the sexagenary cycle, and calendrical use.
- Hong Kong Observatory: The 24 Solar Terms香港天文台二十四節氣資料：節氣以太陽視黃經定位，支月邊界不是西曆月初An official astronomical explanation of the 24 solar terms, their 15-degree divisions along the ecliptic, and the alternating major and minor terms.
- 《禮記・月令》《禮記·月令》孟仲季月與四時政令：寅至丑的季節月序及月令背景An early classical source for the seasonal grouping of Jia-Yi, Bing-Ding, Wu-Ji, Geng-Xin, and Ren-Gui.