BAZI KNOWLEDGE BASE
How to calculate the BaZi Month Pillar: Jie boundaries and Five Tigers
Calculate the Month Pillar in two steps. First locate the birth between two Jie boundaries to find its branch. Then use the Year Stem and the Five Tigers rule to obtain its stem. Yin month is not simply every date in the first lunar month, and the Month Stem does not come directly from the numbered Gregorian month.
First find the branch, beginning with Yin at Li Chun
The starts run as follows: Li Chun (the Start of Spring calendar marker used as the year boundary in many BaZi methods)–Yin, Jing Zhe–Mao, Qing Ming–Chen, Li Xia–Si, Mang Zhong–Wu, Xiao Shu–Wei, Li Qiu–Shen, Bai Lu–You, Han Lu–Xu, Li Dong–Hai, Da Xue–Zi and Xiao Han–Chou. Each lasts until the next Jie.
A birth after Qing Ming and before Li Xia belongs to Chen month. Gu Yu occurs within that interval without changing the branch, and lunar day one does not interrupt it. For a boundary birth, check the term’s time and time zone rather than only the term printed on that date.
Five Tigers: the Year Stem sets Yin month’s starting stem
The month derivation in Sanming Tonghui and the Observatory’s month-stem table give these starting pairs. “Tiger” refers to Yin and “five” to the five groups of Year Stems. From the Yin starting stem, advance one stem per month, returning to Jia after Gui.
| Year Stem | Starting Yin month |
|---|---|
| Jia / Ji | Bing Yin |
| Yi / Geng | Wu Yin |
| Bing / Xin | Geng Yin |
| Ding / Ren | Ren Yin |
| Wu / Gui | Jia Yin |
Work it through: Chen month in a Jia year
Suppose the year has already been established under the Li Chun convention, its stem is Jia, and the birth is after Qing Ming but before Li Xia. The branch is Chen. The Jia/Ji group starts with Bing Yin, followed by Ding Mao and then Wu Chen. The Month Pillar is therefore Wu Chen.
This example supplies only the conditions needed for the Month Pillar, not an invented complete natal chart (the chart calculated for the birth moment). Before Qing Ming it would remain Ding Mao. Passing Gu Yu does not advance it to Ji Si.
January can still belong to the preceding BaZi year’s month sequence
Under a Li Chun year boundary, the interval after Xiao Han and before the next Li Chun is Chou month. Its stem continues the preceding BaZi year’s sequence. Turning the Gregorian calendar from December to January does not introduce a new Year Stem into that sequence.
Li Chun changes the Year Pillar (the two-symbol column for the birth year) and starts the next Yin month together. If two charts disagree on both month characters, check whether their year and month boundaries have been mixed before questioning the starting-stem rule.
Why the month matters, and what the table cannot tell you
The Month Branch (the lower symbol in the birth-month column) places the birth within the seasonal year, before interpretation considers month command (the seasonal conditions represented by the birth month), strength or patterns. Five Tigers joins a year stem to a month branch; it does not rank months as fortunate or unfortunate.
Clarify’s month-stem mapping follows this table, while its Jie crossings come from an approximate solar-position formula. Agreement with the table does not establish second-level boundary accuracy. Records close to a crossing still need separate checking.