BAZI KNOWLEDGE BASE
How to calculate the BaZi Hour Pillar: double hours and Five Rats
The Hour Pillar combines an Hour Branch with an Hour Stem. The branch divides the day into twelve roughly two-hour periods; the Five Rats rule then derives the stem from a Day Stem. Knowing “Si hour” supplies only the second character. Establish which time scale the clock reading uses before applying the tables.
The twelve two-hour periods
The table shows intervals at minute resolution: after the 10:59 minute ends, 11:00 begins Wu hour. It can be applied to civil or solar time, but first obtain the clock reading on the chosen scale. Do not mix the two within one lookup.
| Hour Branch | Clock reading |
|---|---|
| Zi | 23:00–00:59 |
| Chou | 01:00–02:59 |
| Yin | 03:00–04:59 |
| Mao | 05:00–06:59 |
| Chen | 07:00–08:59 |
| Si | 09:00–10:59 |
| Wu | 11:00–12:59 |
| Wei | 13:00–14:59 |
| Shen | 15:00–16:59 |
| You | 17:00–18:59 |
| Xu | 19:00–20:59 |
| Hai | 21:00–22:59 |
Five Rats: start with Zi’s stem, then advance
“Rat” corresponds to Zi, and each of five Day Stem groups has a starting Zi stem. Here the Day Stem means the one the method uses to derive the hour. During ordinary daytime this is usually the displayed Day Stem; late Zi needs its rollover convention checked.
| Day Stem used for the hour | Starting Zi pillar |
|---|---|
| Jia / Ji | Jia Zi |
| Yi / Geng | Bing Zi |
| Bing / Xin | Wu Zi |
| Ding / Ren | Geng Zi |
| Wu / Gui | Ren Zi |
Why 10:30 on a Jia day gives Ji Si
Suppose Jia is the established Day Stem and 10:30 is the final clock reading used by the method. The branch table gives Si. A Jia/Ji day starts at Jia Zi, then Yi Chou, Bing Yin, Ding Mao, Wu Chen and Ji Si. The Hour Pillar is Ji Si.
If 10:30 is only the original civil reading and the method still requires a solar-time correction, complete that first. The example explicitly uses the final lookup time; it does not silently omit time-zone or longitude steps for a real city.
Why a few minutes can matter within two-hour periods
10:50 and 10:55 lie in the same period, but 11:00 starts another. A record of “around eleven” can straddle Si and Wu. The length of a double hour does not make every small uncertainty irrelevant.
With a valid birthplace and known time, Clarify’s full calculation uses corrected solar time for the Hour Branch. During its 23:00 hour, the stem is derived from the day after the entered date, while the displayed Day Pillar (the two-symbol column for the birth day) retains that civil date. This differs from moving the whole chart to the next day at 23:00.
An unknown time need not produce an invented pillar
An absent Hour Pillar leaves its Ten Gods (traditional labels for relationships to the birth-day element), hidden stems (the additional element symbols traditionally assigned inside each lower chart symbol) and interactions unconfirmed. Substituting noon and treating those relationships as established hides the missing information. Keep the supported pillars and identify what cannot yet be assessed.
Five Rats is a stem-branch derivation rule, not a tool for recovering a birth minute from personality. It helps check how a chart obtained an hour stem; it does not prove the birth happened in that interval.