Casting the Four Pillars: How a BaZi Chart Is Built
In a Nutshell
Converting a birth time into four Stem-Branch pairs — Year, Month, Day, and Hour Pillars — is called "casting the chart." BaZi is the *result* of the casting, not a computed destiny.
Quick facts
| Item | Detail |
|---|---|
| Year Pillar | Birth year — boundary is Li Chun (~Feb 4), not Lunar New Year |
| Month Pillar | Birth month — boundaries are the twelve solar terms |
| Day Pillar | Birth date — looked up directly, unaffected by solar terms |
| Hour Pillar | Birth hour — twelve two-hour periods, stem derived from the day stem |
| Day Master | The Day Pillar's stem — the "I" of the chart |
| True Solar Time | Clock time is converted by birthplace longitude before casting |
What each pillar covers (traditional assignment)
| Pillar | Corresponds to | Traditional image (reference) |
|---|---|---|
| Year Pillar | Birth year | Ancestors, family background, early years |
| Month Pillar | Birth month | Parents, youth |
| Day Pillar | Birth date | Self, spouse, middle age |
| Hour Pillar | Birth hour | Children, later years |
The Day Pillar's stem is the Day Master — the "I" of the chart, the benchmark for all Ten Gods.
Year Pillar: Li Chun is the boundary
The year Stem-Branch changes at Li Chun (the start of spring), not on Lunar New Year's Day. Born before Li Chun, you still belong to the previous year's Stem-Branch — e.g., born February 3, 2026 (before Li Chun), your Year Pillar is Yi Si, not Bing Wu. This is the most common chart-casting pitfall.
Month Pillar: solar terms are the boundaries
The twelve month pillars are divided by the twelve "jie" solar terms: Li Chun (Yin month), 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), Xiao Han (Chou).
The month branch is fixed; the month stem is derived from the year stem via the traditional "Wu Hu Dun" mnemonic: "In Jia and Ji years, Bing leads; in Yi and Geng years, Wu heads; Bing and Xin years seek Geng; Ding and Ren years follow Ren's flow; for Wu and Gui years, look above Jia Yin."
Day and Hour Pillars
- Day Pillar: looked up directly in a perpetual calendar, unaffected by solar terms. Note: births around 11 pm fall on a boundary where schools differ slightly — MoZhu standardizes this via True Solar Time conversion.
- Hour Pillar: the day is divided into twelve two-hour periods — Zi 11 pm–1 am, Chou 1–3 am, Yin 3–5 am, Mao 5–7 am, Chen 7–9 am, Si 9–11 am, Wu 11 am–1 pm, Wei 1–3 pm, Shen 3–5 pm, You 5–7 pm, Xu 7–9 pm, Hai 9–11 pm. The hour stem is derived from the day stem via the "Wu Zi Dun" mnemonic: "Jia and Ji days add Jia; Yi and Geng days start with Bing; Bing and Xin days begin at Wu; Ding and Ren days rest at Geng Zi; for Wu and Gui days, Ren Zi is the true path."
True Solar Time
The same Beijing time means a solar position nearly two hours apart between Xinjiang and Shanghai. Precise casting converts clock time to True Solar Time using the birthplace's longitude before fixing the hour's Stem-Branch. MoZhu's casting does this automatically.
How MoZhu does it
MoZhu holds one iron rule: casting is done entirely by precise code; AI only interprets. Stem-Branch derivation, solar-term judgment, Hidden Stem expansion, and Luck Pillar direction are all computed by program — never by a language model's mental arithmetic. Math to math; meaning to meaning.
MoZhu tip
To verify a chart, check three things: the Year Pillar uses the Li Chun boundary, the Month Pillar uses solar-term boundaries, and the hour was converted to True Solar Time. Get those three right and the chart is essentially right.
Classical sources
Chart-casting methods are documented across classical BaZi literature, including the calendrical chapters of traditional almanacs (tong shu).
*For entertainment purposes only.*