The Rat hour (子時) runs from 23:00 to 01:00 and straddles midnight. That raises a question every BaZi practitioner has to answer: if you were born at 23:30, does your day pillar belong to the day that is ending or to the one about to start?
Twelve double hours
BaZi divides the day into twelve two-hour periods, one for each Earthly Branch, starting with the Rat hour. The stem of each hour follows from the stem of the day by the traditional "Five Rats" rule, so the whole hour pillar is fixed once the day pillar is known. All times here are local solar time — see True Solar Time for why your clock time may need correcting first.
| Hour (local solar time) | Branch | Day 甲 or 己 | Day 乙 or 庚 | Day 丙 or 辛 | Day 丁 or 壬 | Day 戊 or 癸 |
|---|---|---|---|---|---|---|
| 23:00–01:00 | 子 Zi Rat | 甲子 | 丙子 | 戊子 | 庚子 | 壬子 |
| 01:00–03:00 | 丑 Chou Ox | 乙丑 | 丁丑 | 己丑 | 辛丑 | 癸丑 |
| 03:00–05:00 | 寅 Yin Tiger | 丙寅 | 戊寅 | 庚寅 | 壬寅 | 甲寅 |
| 05:00–07:00 | 卯 Mao Rabbit | 丁卯 | 己卯 | 辛卯 | 癸卯 | 乙卯 |
| 07:00–09:00 | 辰 Chen Dragon | 戊辰 | 庚辰 | 壬辰 | 甲辰 | 丙辰 |
| 09:00–11:00 | 巳 Si Snake | 己巳 | 辛巳 | 癸巳 | 乙巳 | 丁巳 |
| 11:00–13:00 | 午 Wu Horse | 庚午 | 壬午 | 甲午 | 丙午 | 戊午 |
| 13:00–15:00 | 未 Wei Goat | 辛未 | 癸未 | 乙未 | 丁未 | 己未 |
| 15:00–17:00 | 申 Shen Monkey | 壬申 | 甲申 | 丙申 | 戊申 | 庚申 |
| 17:00–19:00 | 酉 You Rooster | 癸酉 | 乙酉 | 丁酉 | 己酉 | 辛酉 |
| 19:00–21:00 | 戌 Xu Dog | 甲戌 | 丙戌 | 戊戌 | 庚戌 | 壬戌 |
| 21:00–23:00 | 亥 Hai Pig | 乙亥 | 丁亥 | 己亥 | 辛亥 | 癸亥 |
Two rules for the hour before midnight
- Early Rat hour rule (早子時). The new BaZi day begins at 23:00, at the start of the Rat hour. Someone born at 23:30 on 10 March takes the day pillar of 11 March. This keeps each double hour whole and is followed by most modern practitioners. It is Fate Hall's default.
- Late Rat hour rule (夜子時). The day changes at midnight, as on the civil calendar. The hour from 23:00 to 24:00 keeps the day pillar of the day that is ending, and only the hour from 00:00 to 01:00 belongs to the new day.
The choice only matters for births between 23:00 and midnight (in corrected local time). For everyone else both rules give exactly the same chart.
Within the late rule there is a further split: some practitioners keep today's day pillar but take the hour stem from the next day. Fate Hall applies one rule consistently — under the late rule, both the day pillar and the hour stem come from the day that is ending.
What changes in your chart
Moving the day pillar by one day changes your Day Master, so for a 23:00–24:00 birth the two rules can give two quite different readings. The day before and the day after always have neighbouring stems — Jia and Yi, say — so the Day Master often stays within the same element but changes between yang and yin, or moves on to the next element. The hour pillar's stem also changes, because it is derived from the day stem.
The year and month pillars do not change, unless the birth also happens to fall on the day of a solar term.
Which rule should I use?
There is no universal answer. If you have had your chart read before, use the same rule your reader used, so the results are comparable. If not, the early rule is the more common choice today. Fate Hall lets you switch between them in the time settings, and the time-basis panel on the BaZi screen shows both versions side by side whenever they differ.
Common questions
I was born at 00:20. Does any of this apply to me? No. After midnight both rules agree that it is the new day and the Rat hour.
My clock time was 23:10, but the corrected time is 22:40. Which rule applies? Neither: the corrected time falls in the Pig hour (21:00–23:00) of the same day, so both rules give the same chart. The rule is applied after the time correction.
Related guides
- True Solar TimeWhy BaZi uses the Sun's position instead of clock time: longitude correction, the equation of time and daylight saving, with tables for major cities and every month.
- The Sixty Jiazi and NayinAll sixty stem-branch pairs from Jia Zi to Gui Hai, with their animal, Nayin element and years from 1924 to 2043, and how the cycle counts years, months, days and hours.
- The Twelve Earthly BranchesThe twelve branches from Zi (Rat) to Hai (Pig): their element, solar month, double hour and hidden stems, and the harmonies and clashes between them.