The one pillar people most often get wrong is the hour. The year, month and day come straight off a calendar; the hour stem has to be derived from the day stem, and if you skip that step you end up with the wrong final quarter of the chart. This bazi hour stem table gives you every combination on one page, built from the classical shortcut known as the Five Rats rule (五鼠遁 wǔshǔdùn).
What the Five Rats rule (五鼠遁 wǔshǔdùn) actually does
Ba Zi (八字 bāzì) has ten Heavenly Stems and twelve Earthly Branches. Every double-hour already carries a fixed branch — the Rat hour is always 子 (Zǐ), the Horse hour is always 午 (Wǔ) — but the stem sitting on top of that branch changes depending on which day you were born. The Five Rats rule is simply the memory device that tells you which stem starts the day.
The name comes from the Rat: the day always begins at the Rat hour (子時), so if you know the stem of that first Rat hour, you count the remaining eleven hours forward through the stem sequence and the whole day is solved. Five “rats” because the ten day stems fold into five starting points — the pairs 甲/己, 乙/庚, 丙/辛, 丁/壬 and 戊/癸 each begin their day on the same Rat-hour stem.
The complete hour stem table (all 60 pillars)
Read down the left column to find your day stem pair, then across to the hour branch. The cell is the full hour pillar in hanzi.
| Day stem | 子 Zǐ | 丑 Chǒu | 寅 Yín | 卯 Mǎo | 辰 Chén | 巳 Sì | 午 Wǔ | 未 Wèi | 申 Shēn | 酉 Yǒu | 戌 Xū | 亥 Hài |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 甲 / 己 (Jiǎ or Jǐ) | 甲子 | 乙丑 | 丙寅 | 丁卯 | 戊辰 | 己巳 | 庚午 | 辛未 | 壬申 | 癸酉 | 甲戌 | 乙亥 |
| 乙 / 庚 (Yǐ or Gēng) | 丙子 | 丁丑 | 戊寅 | 己卯 | 庚辰 | 辛巳 | 壬午 | 癸未 | 甲申 | 乙酉 | 丙戌 | 丁亥 |
| 丙 / 辛 (Bǐng or Xīn) | 戊子 | 己丑 | 庚寅 | 辛卯 | 壬辰 | 癸巳 | 甲午 | 乙未 | 丙申 | 丁酉 | 戊戌 | 己亥 |
| 丁 / 壬 (Dīng or Rén) | 庚子 | 辛丑 | 壬寅 | 癸卯 | 甲辰 | 乙巳 | 丙午 | 丁未 | 戊申 | 己酉 | 庚戌 | 辛亥 |
| 戊 / 癸 (Wù or Guǐ) | 壬子 | 癸丑 | 甲寅 | 乙卯 | 丙辰 | 丁巳 | 戊午 | 己未 | 庚申 | 辛酉 | 壬戌 | 癸亥 |
The formula behind the table
If you would rather compute than look up, the arithmetic is exact. Index the stems 甲=0 through 癸=9 and the branches 子=0 through 亥=11, then:
hour-stem index = (day-stem index mod 5) × 2 + hour-branch index, mod 10.
That single line generates the whole grid. The “mod 5” is why the day stems pair up into five columns; the “× 2” is why each new day advances the Rat-hour stem by two places.
Worked example
Say the day pillar is a Jia 甲 day and the birth time is 11:40. Eleven-forty falls inside the Horse hour (午, 11:00–12:59), branch index 6. Jia is stem index 0, so (0 mod 5) × 2 + 6 = 6, and stem index 6 is 庚 (Gēng). The hour pillar is therefore 庚午 (Gēng Wǔ) — which is exactly what you read off the 甲/己 row under the 午 column above.
Why the stem matters: the hour as a ten-god seat
The hour is the destination pillar of the chart. In classical palace terms it governs children, creative output, ambition and later life — the chapters you are still writing. The branch of that pillar is fixed by the clock, so the stem this table delivers is precisely the part that differs from person to person, and it carries real interpretive weight: the hour stem plays a Ten God (十神 shíshén) against your Day Master, and that god describes what sits at your destination.
Continue the worked example. For a Jia Day Master, the 庚 on 庚午 is Seven Killings (七杀 qīshā) — pressure, command, demands at the destination. Now notice that a Ji 己 day produces the identical pillar 庚午 at the same hour, because Jia and Ji share a row; but for a Ji Day Master 庚 is Hurting Officer (伤官 shāngguān), a completely different reading. The shared column saves memorisation, not interpretation — the same sixty pillars land differently on each of the ten Day Masters.
Finding your hour pillar in four steps
- Fix the day stem. It is the upper character of your day pillar — the same character as your Day Master. If you have never plotted the chart, the reading-order guide shows where each of the eight characters sits.
- Convert the birth time to a branch. Each double-hour owns a fixed branch; the column headers above give all twelve. A 07:30 birth is the Dragon hour 辰, an 18:10 birth is the Rooster hour 酉.
- Cross the row and column. Day stem row, hour branch column — the cell is your hour pillar, stem and branch complete.
- Check the edges. If the birth time sits within roughly twenty minutes of an hour boundary, or anywhere between 23:00 and 00:59, read the late-Zi section below and confirm with a solar-time-corrected calculation before trusting the result.
The late Zi (子) convention — read this before you finalise
The Rat hour spans 23:00–00:59, which straddles midnight. That creates the single most argued-over question in hour reckoning: what happens to a birth between 23:00 and 23:59? On this site the standing convention is the late-Zi (晚子時 wǎn zǐshí) rule — the hour pillar takes the next day’s stem for its Rat hour, while the day pillar stays with the calendar day you were actually born on. Schools genuinely differ here; some keep both the day and the hour on the old day. We explain the full reasoning, and how to test which reading fits a chart, on the birth hour and hour pillar page.
If the birth time is unknown
A missing birth time does not make a chart useless — it makes it three-quarters of a chart. The year, month and day pillars still carry the season, the Day Master and the spouse palace, and most strength judgements survive on those six characters. What you lose is the children and later-life palace and one ten-god seat, so hold any conclusions in those areas loosely. Before giving up, check the sources people forget: hospital records, baby books, a parent’s memory anchored to mealtimes or television schedules. When a time can only be narrowed to two or three candidate double-hours, a practitioner works backwards — each candidate produces a different hour pillar from this table, and known life events are tested against each version until one fits. Guessing noon by default is the one habit to avoid; it quietly plants a specific stem and branch that were never yours.
Going deeper by day stem
Each day stem has its own dedicated page with the twelve hour pillars laid out against real clock times, so you can go straight to yours: the Jia day hour table, the Bing day hour table, or the Gui day hour table among the ten. To see how the branch itself colours a chart, the Rat hour page is the place to start, and the stems and branches guide covers the 22-character alphabet the whole grid is built from.
Or skip the table entirely — find your hour pillar to the minute by plotting your chart free with the calculator, which handles the Five Rats derivation and the late-Zi convention for you.