The BaZi Hour Pillar: The Period Sets the Branch, the Five Rats Set the Stem
The hour pillar works much like the month pillar: the branch comes from the time, and the stem comes from a verse, this time starting from the day stem. The one thing to watch is that the hour stem follows the day, so if the day pillar is wrong, the hour pillar will be wrong too.
Step one: the two-hour period gives the branch
| Period | Time |
|---|---|
| Zi (子) | 23:00–00:59 (from 23:00 it is the Late Zi hour) |
| Chou (丑) | 01:00–02:59 |
| Yin (寅) | 03:00–04:59 |
| Mao (卯) | 05:00–06:59 |
| Chen (辰) | 07:00–08:59 |
| Si (巳) | 09:00–10:59 |
| Wu (午) | 11:00–12:59 |
| Wei (未) | 13:00–14:59 |
| Shen (申) | 15:00–16:59 |
| You (酉) | 17:00–18:59 |
| Xu (戌) | 19:00–20:59 |
| Hai (亥) | 21:00–22:59 |
Use the local time of the birthplace. If you were born under daylight saving time, take off the hour first; the more careful approach also converts to true solar time. See birth time correction.
Step two: the Five Rats rule gives the stem
Five Rats (五鼠遁, wu shu dun): from the day stem to the Zi hour stem
甲己還加甲，乙庚丙作初，丙辛從戊起，丁壬庚子居，戊癸何方發，壬子是真途。
The "rat" is the Zi (子) hour, the first hour of the BaZi day. The verse names the stem that hour takes on each kind of day: on a Jia or Ji day the Zi hour begins with Jia; Yi or Geng, with Bing; Bing or Xin, with Wu; Ding or Ren, with Geng; Wu or Gui, with Ren.
In other words, on a Jia or Ji day the Zi hour is Jia-Zi, on a Yi or Geng day it is Bing-Zi, and so on. Each period after that moves the stem on by one.
| Day stem | Zi 子 | Chou 丑 | Yin 寅 | Mao 卯 | Chen 辰 | Si 巳 | Wu 午 | Wei 未 | Shen 申 | You 酉 | Xu 戌 | Hai 亥 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Jia or Ji day 甲、己 | 甲子 Jia-Zi | 乙丑 Yi-Chou | 丙寅 Bing-Yin | 丁卯 Ding-Mao | 戊辰 Wu-Chen | 己巳 Ji-Si | 庚午 Geng-Wu | 辛未 Xin-Wei | 壬申 Ren-Shen | 癸酉 Gui-You | 甲戌 Jia-Xu | 乙亥 Yi-Hai |
| Yi or Geng day 乙、庚 | 丙子 Bing-Zi | 丁丑 Ding-Chou | 戊寅 Wu-Yin | 己卯 Ji-Mao | 庚辰 Geng-Chen | 辛巳 Xin-Si | 壬午 Ren-Wu | 癸未 Gui-Wei | 甲申 Jia-Shen | 乙酉 Yi-You | 丙戌 Bing-Xu | 丁亥 Ding-Hai |
| Bing or Xin day 丙、辛 | 戊子 Wu-Zi | 己丑 Ji-Chou | 庚寅 Geng-Yin | 辛卯 Xin-Mao | 壬辰 Ren-Chen | 癸巳 Gui-Si | 甲午 Jia-Wu | 乙未 Yi-Wei | 丙申 Bing-Shen | 丁酉 Ding-You | 戊戌 Wu-Xu | 己亥 Ji-Hai |
| Ding or Ren day 丁、壬 | 庚子 Geng-Zi | 辛丑 Xin-Chou | 壬寅 Ren-Yin | 癸卯 Gui-Mao | 甲辰 Jia-Chen | 乙巳 Yi-Si | 丙午 Bing-Wu | 丁未 Ding-Wei | 戊申 Wu-Shen | 己酉 Ji-You | 庚戌 Geng-Xu | 辛亥 Xin-Hai |
| Wu or Gui day 戊、癸 | 壬子 Ren-Zi | 癸丑 Gui-Chou | 甲寅 Jia-Yin | 乙卯 Yi-Mao | 丙辰 Bing-Chen | 丁巳 Ding-Si | 戊午 Wu-Wu | 己未 Ji-Wei | 庚申 Geng-Shen | 辛酉 Xin-You | 壬戌 Ren-Xu | 癸亥 Gui-Hai |
Generated by our engine. For the Late Zi hour (after 23:00) the day pillar has already moved to the next day, so the hour stem is also worked out from the next day's stem.
Worked example: March 12, 1985, You hour
Born March 12, 1985 (Gregorian), 5–7 p.m.
- ① Year pillar: in 1985 the Start of Spring fell at 1985-02-04 05:11; March 12 is after it, so use 1985. (1985 − 4) ÷ 10 leaves 1 → stem number 2, Yi (乙); ÷ 12 leaves 1 → branch number 2, Chou (丑). Year pillar: Yi-Chou (乙丑).
- ② Month pillar: the last jie term before the birth was the Awakening of Insects (1985-03-05 23:16), so the month branch is Mao. For a Yi year the Five Tigers verse says "in Yi and Geng years, Wu leads," so the Yin month is Wu-Yin; count 1 on to Mao, and the month pillar is Ji-Mao (己卯).
- ③ Day pillar: January 1, 2000 was Wu-Wu (number 55, index 54). March 12, 1985 is 5408 days earlier: (54 − 5408) divided by 60 leaves 46, which is number 47, so the day pillar is Geng-Xu (庚戌).
- ④ Hour pillar: for a Geng day the Five Rats verse says "Yi and Geng begin with Bing," so the Zi hour is Bing-Zi; count 9 on to You, and the hour pillar is Yi-You (乙酉).
If you don't know the hour
Without the hour you can only cast three pillars. What still holds and what changes is covered in unknown birth hour.
Watch your chart being worked out, step by step
Enter your Gregorian birthday and hour. The tool follows the method on this page and shows how each of the year, month, day and hour pillars is calculated, then checks the result against our chart engine. Everything is calculated in your browser; nothing is uploaded.
Uses your Gregorian birthday, with the day changing at 11 p.m.; the solar terms are compared at the middle of your two-hour period (as in our main chart calculator).
A straight word: working it by hand is for understanding, not for replacing a calculator
Once you have worked a chart by hand, you know where every character in it comes from, and you can read other people's charts with more confidence. Real charts, though, turn on the exact moment of a solar term, daylight saving time and true solar time, and one slip costs you a whole pillar. When you are done, check it once with a calculator. Everything on this site is for reference and entertainment.
Work out your hour pillar
Enter your birthday and hour, and the tool works out your hour pillar with the Five Rats rule, step by step.
Hour pillar FAQ
How do you calculate the BaZi hour pillar?
The branch follows the two-hour period of birth; the stem comes from the Five Rats rule, which gives the Zi hour stem from the day stem, and then moves on one step per period.
What is the Five Rats verse?
The verse (甲己還加甲，乙庚丙作初，丙辛從戊起，丁壬庚子居，戊癸何方發，壬子是真途。) says: on a Jia or Ji day the Zi hour begins with Jia; Yi or Geng, with Bing; Bing or Xin, with Wu; Ding or Ren, with Geng; Wu or Gui, with Ren.
I was born under daylight saving time. How do I work out the hour pillar?
Subtract one hour from the time on the birth certificate to get back to standard time, then find the two-hour period.