Chart methods and reference
How solar terms set the BaZi month pillar: jie boundaries explained
The BaZi month branch follows solar-term months rather than the first day of a lunar month. At a boundary, the instant of the term matters, not merely the date printed on a calendar.
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Calculate my BaZi chartLunar months and BaZi months serve different purposes
Lunar calendar months combine new moons and major solar terms. This project’s Four Pillars instead divide the year at the twelve jie: Start of Spring opens Yin month, Awakening of Insects opens Mao, and the sequence continues. Intermediate terms such as Spring Showers and the equinox do not change its month pillar. Yin month can start while the lunar calendar still shows the previous year’s twelfth month. A leap lunar month does not add a thirteenth pillar month.
The branch follows jie; the stem also depends on the year
The table shows month-branch starting terms, not fixed Gregorian dates. The month stem follows the Five Tiger rule from the year stem, whose year changes at Start of Spring. For a Jia year, Yin month begins with Bing Yin, followed by Ding Mao and Wu Chen. Between Moderate Cold and Start of Spring, Chou month still belongs to the previous pillar year. Advancing the year stem on January 1 before deriving the month is inconsistent with this implementation.
| Solar term | Month pillar |
|---|---|
| Start of Spring | Yin |
| Awakening of Insects | Mao |
| Bright and Clear | Chen |
| Start of Summer | Si |
| Grain in Ear | Wu |
| Moderate Heat | Wei |
| Start of Autumn | Shen |
| White Dew | You |
| Cold Dew | Xu |
| Start of Winter | Hai |
| Heavy Snow | Zi |
| Moderate Cold | Chou |
Compare the same absolute instant
The Go engine obtains second-level solar-term times from lunar-go and compares the birth instant against them. The table displays UTC+08:00. Another time zone expresses the same instant with a different clock reading; longitude does not make the event happen earlier. True solar time supplies this project’s day and hour pillars. Correcting the clock and then treating that reading as Beijing time for the term comparison would change the reference twice.
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Calculate my BaZi chartReproduce the Start of Spring and Insects boundaries
These values were generated by the project engine; the boundary instant belongs to the new month. One second before Start of Spring in 2024, the result is Gui Mao year and Yi Chou month. At the boundary it becomes Jia Chen year and Bing Yin month. Awakening of Insects changes only the month to Ding Mao. The seconds are implementation outputs, not a claim of second-level verification by Hong Kong Observatory; astronomical models, rounding and birth-record precision must be assessed separately.
| Solar term | Time (UTC+08:00) | Year pillar | Month pillar |
|---|---|---|---|
| Start of Spring | 2024-02-04 16:27:06 | Gui Mao | Yi Chou |
| Start of Spring | 2024-02-04 16:27:07 | Jia Chen | Bing Yin |
| Awakening of Insects | 2024-03-05 10:22:44 | Jia Chen | Bing Yin |
| Awakening of Insects | 2024-03-05 10:22:45 | Jia Chen | Ding Mao |
When the birth time is too imprecise
If a record only says “after four in the afternoon” and the solar term falls within that interval, retain both candidate month pillars and seek the original record. Assigning the entire day to the new month creates a boundary error, while substituting a Gregorian or lunar month is also unsuitable. These examples establish only the displayed inputs, not all dates, astronomical models or traditional schools.
Why the first lunar day is not the month-pillar boundary
A lunar month begins with the new-moon calendar date. A BaZi month pillar changes at one of the twelve Jie solar-term instants. These are different boundaries, so a lunar month can contain a BaZi month change. Compare the exact Jie instant before deciding which month branch to use.