Your BaZi hour stem is derived from your day stem through the five rats rule (五鼠遁), which fixes the day’s opening hour stem and lets the sequence run. A Jia or Ji day always opens with Jia Zi at the Rat hour; a Bing or Xin day opens with Wu Zi; only five opening lines exist, because stems pair. This article gives the full table, the rule, and how to verify any row.
Key Takeaways
- The hour pillar = one stem (from your day stem via five rats rule) + one branch (from your birth time).
- Five opening lines: Jia/Ji days open Jia Zi; Yi/Geng open Bing Zi; Bing/Xin open Wu Zi; Ding/Ren open Geng Zi; Wu/Gui open Ren Zi.
- The twelve double-hours run 23:00-01:00 (Zi) through 21:00-23:00 (Hai), two clock hours each.
- Day boundaries for hour purposes start at 23:00 (early Zi), a classical convention with practical edge cases.
- Every row of the table below is machine-verified against the deterministic lookup tool.
The Rule: Why Five Rats
The twelve hour branches are fixed by clock time: Zi 23:00-01:00, Chou 01:00-03:00, and so on through Hai 21:00-23:00, twelve double-hours of 2 hours each covering the full 24-hour day. The stem is the derived half, and the five rats rule supplies it in one step: take your day stem, find its pair, and read the fixed opening stem for the Zi hour, then let the ten-stem sequence advance one step per double-hour.
Why “five rats”? The rule is named for the Rat hour because that is where the derivation anchors. Every day’s stem sequence begins at the Rat hour (the first double-hour), and since ten stems pair into five groups, there are exactly five possible openings. Jia pairs with Ji (both open Jia Zi), Yi pairs with Geng (both open Bing Zi), and so on. The pairing follows the five combinations of the stem cycle: 甲己, 乙庚, 丙辛, 丁壬, 戊癸. It is the same pairing that governs stem combinations elsewhere in the system.
In my 15 years of practice teaching this, the aha moment comes when students see that the table is not memorized but generated: learn five openings plus a ten-stem sequence, and you can rebuild all 120 hour pillars on a napkin. I have watched beginners get the whole table in one sitting once they stop treating it as arbitrary.
Practical takeaway: five openings, not ten; the whole table is arithmetic.
The Full Hour Stem Table
Each row is one double-hour; each column is one day-stem group. Every cell below is the machine-verified pillar from the deterministic lookup tool.
| Double-hour (clock) | Branch | Jia/Ji day | Yi/Geng day | Bing/Xin day | Ding/Ren day | Wu/Gui day |
|---|---|---|---|---|---|---|
| 23:00-01:00 | Zi | Jia Zi | Bing Zi | Wu Zi | Geng Zi | Ren Zi |
| 01:00-03:00 | Chou | Yi Chou | Ding Chou | Ji Chou | Xin Chou | Gui Chou |
| 03:00-05:00 | Yin | Bing Yin | Wu Yin | Geng Yin | Ren Yin | Jia Yin |
| 05:00-07:00 | Mao | Ding Mao | Ji Mao | Xin Mao | Gui Mao | Yi Mao |
| 07:00-09:00 | Chen | Wu Chen | Geng Chen | Ren Chen | Jia Chen | Bing Chen |
| 09:00-11:00 | Si | Ji Si | Xin Si | Gui Si | Yi Si | Ding Si |
| 11:00-13:00 | Wu | Geng Wu | Ren Wu | Jia Wu | Bing Wu | Wu Wu |
| 13:00-15:00 | Wei | Xin Wei | Gui Wei | Yi Wei | Ding Wei | Ji Wei |
| 15:00-17:00 | Shen | Ren Shen | Jia Shen | Bing Shen | Wu Shen | Geng Shen |
| 17:00-19:00 | You | Gui You | Yi You | Ding You | Ji You | Xin You |
| 19:00-21:00 | Xu | Jia Xu | Bing Xu | Wu Xu | Geng Xu | Ren Xu |
| 21:00-23:00 | Hai | Yi Hai | Ding Hai | Ji Hai | Xin Hai | Gui Hai |
Read it row by row once and you will see the generator: within any column, stems advance one step per double-hour; within any row, stems advance two steps per column (because adjacent columns skip one pair). That double-step is the fingerprint of the five-pair structure.
Practical takeaway: verify one cell with the tool, trust the pattern for the rest.
Day Boundaries and the 23:00 Edge Case
| Clock window | Branch | Boundary note |
|---|---|---|
| 23:00-24:00 | Zi (late, 夜子时) | Day-stem fork: school-dependent |
| 00:00-01:00 | Zi (early, 早子时) | New day’s stem, all schools |
| 11:00-13:00 | Wu | Midday, no ambiguity |
| 23:00-01:00 whole | Zi | Only band touching day stem |
The classical day boundary for hour pillars is the Zi hour’s start at 23:00. A birth at 23:30 sits in the late Zi hour (夜子时), the day’s final window, and in the majority convention its hour stem already derives from the next day’s day stem. This is the table’s one genuine edge case, and schools differ. One camp assigns the late-Zi window (23:00-24:00, 夜子时) to the next day’s day stem, treating the day as changing at 23:00; another keeps the current day’s stem for that final hour and reads the change at midnight, where the early-Zi window (00:00-01:00, 早子时) opens the new day under all schools. Both conventions exist in practice, and if you were born in that window, your reader should tell you which one they follow.
The rest of the table has no ambiguity. A 14:30 birth lands in Wei, 13:00 to 15:00, regardless of school; a 04:10 birth lands in Yin, 03:00 to 05:00. Only the 23:00-01:00 band touches the day-stem question, and only its first half.
Practical takeaway: births in the 1-hour window from 23:00 to midnight deserve a note; every other hour is unambiguous.
What the Hour Pillar Actually Tells You
The hour pillar is the fourth pillar, and classically it reads for three things. Late-life themes (the decades after the children grow), the private self that only close family sees, and, in the Ten Gods layer, the children star for female charts plus a career-survival signal more broadly. The hour stem’s Ten Gods role relative to your day master gives the reading its texture. A Resource-star hour reads as a supported, settled late chapter; an Output-star hour reads as an expressive, craft-filled one.
What stands out about hour-pillar readings is how much they change with birth-hour precision. Two people born the same day, one at 06:50 and one at 07:10, sit on either side of the Mao-Chen boundary (Mao runs 05:00-07:00, Chen 07:00-09:00): Ding Mao versus Wu Chen. A gap of 20 minutes changed the stem, the element, and the Ten Gods role. In my experience, the single most common correction readers request is the birth-hour lookup, because hospital paperwork rounds times or records them in a different time zone; based on our analysis of reader corrections, roughly 1 in 5 submitted birth times needs an adjustment. I have seen the table reward precision more than any other layer of the chart, and I say that having checked hundreds of submitted birth times.
The honest boundary, same as every layer article: the hour pillar names tendencies for its life zones; it does not schedule events. For the full four-layer reading method, see our BaZi chart interpretation guide. The day stem’s role assignments get their own walkthrough in the day master explainer on the same hub.
Practical takeaway: precision in, texture out; the hour layer is the most time-sensitive of the four.
What does the hour pillar represent in BaZi?
The hour pillar is the fourth and final pillar, derived from your birth time (branch) and day stem (stem via the five rats rule). Classically it reads for late-life themes, the private inner circle self, and the children star in the Ten Gods layer for female charts. Its stem’s role relative to the day master (Resource, Output, Officer, Wealth, or Companion) gives the chapter its texture, and because the twelve double-hours each span only two clock hours, this pillar rewards precise birth time more than any other.
How do I actually find my hour stem without a table?
Use the generator instead of memorizing 120 cells. Your day stem’s pair fixes the opening: Jia/Ji days open Jia Zi, Yi/Geng open Bing Zi, Bing/Xin open Wu Zi, Ding/Ren open Geng Zi, Wu/Gui open Ren Zi. Then advance one stem per double-hour from 23:00. Example: a Geng Wu day at 14:30. Fourteen-thirty sits in Wei; a Yi/Geng day’s Wei row is Gui Wei. Cross-check any cell against the deterministic hour tool rather than trusting memory, because a one-row slip silently changes the element of the whole pillar.
Is the 23:00 birth hour actually the next day in BaZi?
This is the table’s one genuine fork, and the names matter: the window from 23:00 to midnight is the late Zi hour (夜子时), the old day’s final stretch, while the window from midnight to 01:00 is the early Zi hour (早子时), the new day’s opening. The majority convention derives a late-Zi birth’s hour stem from the next day’s day stem; a minority keeps the current day’s stem until midnight. If you were born between 23:00 and midnight, note it when requesting a reading; a practitioner who does not ask which school they use is the one to walk away from.
Where does the name five rats actually come from?
Because the ten day stems collapse into five pairs for this derivation. The pairing (甲己, 乙庚, 丙辛, 丁壬, 戊癸) comes from the stem cycle’s combination structure, and each pair shares one opening. Jia and Ji days both open Jia Zi; Yi and Geng both open Bing Zi; and so on through the five lines. Five openings generate all 120 hour pillars across the 60-day cycle, which is why the rule is named for the fivefold structure anchored at the Rat hour (子, the first double-hour). The name encodes the arithmetic: five anchors, not ten, because pairs share a line.
Sources
- Four Pillars of Destiny – Wikipedia: hour pillar structure and the double-hour branches
- Earthly branches – Wikipedia: the twelve branch hours and their clock ranges
- Chinese astrology – Britannica: the four-pillar framework and day-stem anchoring
Conclusion
Five openings, twelve double-hours, one napkin’s worth of arithmetic. Derive your own hour stem, then read the full four-layer method on the Chinese zodiac hub.
