Structure · the fourth pillar

The Hour Pillar, Explained

The hour branch is set by which two-hour block you were born in, and the hour stem follows from the day stem by a rule with five starting points. Twelve blocks against five starting points is exactly sixty — the same sixty pillars the day cycle uses.

The twelve blocks and their clock windows

The twelve branches each occupy two hours. Note that the Zi block straddles midnight: it begins at 23:00, not at 00:00.

Hour branchClock windowBranch elementHidden stems (main qi first)
子 Zi, Rat23:00–01:00Water癸
丑 Chou, Ox01:00–03:00Earth己 癸 辛
寅 Yin, Tiger03:00–05:00Wood甲 丙 戊
卯 Mao, Rabbit05:00–07:00Wood乙
辰 Chen, Dragon07:00–09:00Earth戊 乙 癸
巳 Si, Snake09:00–11:00Fire丙 庚 戊
午 Wu, Horse11:00–13:00Fire丁 己
未 Wei, Goat13:00–15:00Earth己 丁 乙
申 Shen, Monkey15:00–17:00Metal庚 壬 戊
酉 You, Rooster17:00–19:00Metal辛
戌 Xu, Dog19:00–21:00Earth戊 辛 丁
亥 Hai, Pig21:00–23:00Water壬 甲

How the hour stem is set: five starting points

The rule is one line: the day stem fixes the stem of the Zi hour, and the rest follow the blocks in order. The table below is not a copied mnemonic — it was produced by computing every day from 1984 onward until all ten day stems had been observed, and the build asserts that the two stems in each group agree.

Day-stem groupStem of the Zi hourComputed sample
甲 Jia · 己 Ji甲 Jia1984-01-01 → 甲午 Jia Wu · 甲子 Jia Zi
乙 Yi · 庚 Geng丙 Bing1984-01-02 → 乙未 Yi Wei · 丙子 Bing Zi
丙 Bing · 辛 Xin戊 Wu1984-01-03 → 丙申 Bing Shen · 戊子 Wu Zi
丁 Ding · 壬 Ren庚 Geng1984-01-04 → 丁酉 Ding You · 庚子 Geng Zi
戊 Wu · 癸 Gui壬 Ren1984-01-05 → 戊戌 Wu Xu · 壬子 Ren Zi

Five starting points, each walking twelve blocks, give 5 × 12 = 60 hour pillars — exactly the sixty-pillar cycle, no more and no less. The build checks that identity, so the table cannot be half right.

The example day in all twelve blocks

The example chart is 1985-07-04, a 甲辰 Jia Chen day (day stem 甲). The same chart born at dawn, at noon or at night has a completely different fourth pillar:

BlockHour pillarHour stem
子 Zi, Rat甲子 Jia Zi甲 Jia
丑 Chou, Ox乙丑 Yi Chou乙 Yi
寅 Yin, Tiger丙寅 Bing Yin丙 Bing
卯 Mao, Rabbit丁卯 Ding Mao丁 Ding
辰 Chen, Dragon戊辰 Wu Chen戊 Wu
巳 Si, Snake己巳 Ji Si己 Ji
午 Wu, Horse庚午 Geng Wu庚 Geng
未 Wei, Goat辛未 Xin Wei辛 Xin
申 Shen, Monkey壬申 Ren Shen壬 Ren
酉 You, Rooster癸酉 Gui You癸 Gui
戌 Xu, Dog甲戌 Jia Xu甲 Jia
亥 Hai, Pig乙亥 Yi Hai乙 Yi

The 23:00 boundary

The late Zi hour belongs to the next day under the mainstream convention, so the day pillar and the hour pillar move together. Two births two minutes apart can land on different day pillars:

Birth momentDay pillarHour pillar
22:58甲辰 Jia Chen乙亥 Yi Hai
23:00乙巳 Yi Si丙子 Bing Zi

This site defaults to sect=1 (the day rolls over); the other school (sect=0) gives day 甲辰 (Jia Chen) at the same moment. Both are documented on the methodology page; this page only pins the boundary to the minute.

The hour pillar is not a personality label

The popular version pairs each two-hour block with a personality, as if two hours could settle a person. Structurally the hour pillar is a position: it carries a stem and a branch, two ten-god labels, two characters of five-element weight, and it supplies the moment the luck-cycle conversion needs. All of that can be checked item by item. "People born in the Zi hour are like this" cannot, and this page does not print it.

What this site claims

A note on what this page deliberately does not do: the popular versions of this material assign a fixed personality to each term — one character per branch, one destiny per stage. This site rejects that framing. What is published here is a structural position: which element sits where, on what kind of ground, with which tenants inside. The same term reads differently under a different month command, and no meaningful judgement exists without the other characters of the chart. Where the tradition offers a reading it is labelled as the tradition's; this site's own contribution is that every number and term on this page is computed, versioned and checkable against the methodology page.

Frequently asked

These are the questions specific to this page; broader conventions live on the methodology page.

Is the hour pillar two hours wide in real time?
In clock time, yes. Under true solar time the same clock reading can belong to a neighbouring block depending on longitude, because an administrative time zone can be up to two hours of solar time away from its meridian.
Why does the late Zi hour change the day pillar?
Because under the mainstream convention the day itself rolls over at 23:00, not at midnight. If you were born between 23:00 and 23:59 the day pillar, the hour pillar and the day master all move together.
Where does the five-starting-point rule come from?
From the classical mnemonic for the hour stem. This site does not copy the mnemonic: it derives the five starting points by computing day stems from 1984 onward and asserting the two day stems in each group agree, then checks that five groups times twelve blocks equals the sixty-pillar cycle.
Do I need the hour for anything else?
The luck-cycle start age, which converts the distance between the birth moment and the adjacent solar term. Everything else on the chart is computed from the date alone.

Reference index

Every enumerable component of ba zi has its own page here. Each page is computed by the same engine and can be checked item by item — none of it is a personality table.