Early and Late Zi Hour: Born After 11 p.m., Is Your Day Pillar Today or Tomorrow?
Of the twelve two-hour periods, only the Zi hour crosses midnight. Its first half falls in the 23:00 hour of one day and its second half in the 0:00 hour of the next. The trouble is the first half: for someone born in that hour, which day does the day pillar belong to? Different answers give different Day Masters, and every Ten God and favorable element in the chart moves with them.
The two schools
| Day changes at 23:00 (zi chu) | Day changes at midnight (ye zi shi school) | |
|---|---|---|
| Born 23:00–23:59 | Day pillar is the next day's, hour pillar derived from the next day's stem | Day pillar is that day's; the hour pillar is handled differently by different teachers (from the next day's stem or the same day's) |
| Born 00:00–00:59 | Day pillar is that day's | Day pillar is that day's |
| Reasoning | A day has twelve hours starting with Zi; when Zi begins, so does the new day | The calendar date changes at midnight, and the chart should match civil dates |
| This site | Our choice | The tool lists this school's day pillar as well |
How we counted: our engine drew random birth times (to the minute) within each period, 12,000 per group, and compared the four pillars cast straight from the clock hour with the exact, corrected pillars. The modern Taiwan group was born 1980–2010; the daylight-saving group, 1946–1979.
The schools disagree about a single hour, but plenty of people are born in it. The harder part is that correction can push a birth into or out of that hour. A 0:30 a.m. birth under daylight saving time becomes 23:30 the previous day once the hour comes off; true solar time can move 22:55 to 23:05.
The Late Zi hour: two schools, two Day Masters
Born December 31, 1985, 11:20 p.m., Kaohsiung
- True solar time: Kaohsiung's longitude offset is +1 minutes and the equation of time −4 minutes, giving 23:17. That is still in the 23:00 hour: the Late Zi hour.
- Day changes at 23:00 (our choice): the Day Pillar belongs to January 1, 1986: Yi-Si (乙巳), a Yi Wood Day Master.
- Day changes at midnight: the Day Pillar stays on December 31: Jia-Chen (甲辰), a Jia Wood Day Master. The two schools give Day Masters of different elements, and every Ten God and favorable element downstream changes with them.
Three ways a correction crosses 23:00
- Born 0:xx a.m. under daylight saving time: taking off the hour gives 23:xx the previous day, the Late Zi hour. Since we change the day at 23:00, the day pillar stays on the certificate date and the hour stays Zi, so nothing changes. For the midnight school, the day pillar moves back one day.
- Clock 22:5x, true solar time past 23:00: the hour moves from Hai into Zi, and under our rule the day pillar moves to the next day as well.
- Clock 23:0x, true solar time back before 23:00: the hour drops from Late Zi back to Hai, and the day pillar returns to that day.
The tool on this page detects all of these and, for a Late Zi birth, shows the day pillar under both schools.
Which school should you trust?
Both have a lineage, and there is no settled answer. In practice, cast both charts and compare: which Day Master's description sounds more like you, and which chart's past luck pillars fit what actually happened? For reading the Day Master, see the ten Day Masters.
Correct your birth time
Enter the Gregorian date, time and place from the birth certificate. The tool works through daylight saving time, the longitude offset, the equation of time, the Zi-hour day change and the solar term boundary in one go, then compares the result pillar by pillar with a chart cast straight from the clock hour. Everything is calculated in your browser; nothing is uploaded.
Enter the clock time exactly as the birth certificate shows it; the tool takes off daylight saving time itself, so do not subtract it first. The day changes at 11 p.m. If your birthplace is not listed, pick the city closest in longitude (one degree is only four minutes).
A straight word: correction only helps if the recorded time is accurate
Hospital records usually give the minute, but family memory is more often "a bit after nine in the morning." If the time could be ten or twenty minutes out, fine-tuning it is pointless. If your time is an estimate, rather than worrying about whether to correct it, cast both possible hours and see which chart sounds more like you. Everything on this site is for reference and entertainment.
Were you born in the Late Zi hour?
Enter the time and place from your birth certificate. The tool works out true solar time and, if it lands in the Late Zi hour, shows the day pillar under both schools.
Early and Late Zi hour FAQ
Born at 11 p.m.: which day counts in BaZi?
It depends on the school. Those who change the day at 23:00 use the next day; those who change it at midnight use the same day. We change the day at 23:00, and our tool lists the other school's day pillar too.
What is the difference between the Early and Late Zi hour?
The Early Zi hour is 00:00–00:59; its day pillar is that day's and both schools agree. The Late Zi hour is 23:00–23:59, and the schools differ on whether it takes that day's or the next day's day pillar.
Born at 0:30 a.m. under daylight saving time: Early or Late Zi?
With the daylight-saving hour taken off, it is 23:30 the previous day, which is the Late Zi hour. Because we change the day at 23:00, the day pillar is still the date on the birth certificate.
The two schools give me different Day Masters. Which should I read?
Both have a lineage. Cast both charts and compare the personality descriptions and your past luck pillars with your own experience to see which fits better.