Your "birth eight characters" are the year, month, day and hour of birth written as stems and branches. Software does it in seconds, but knowing the method helps you read a chart and spot common errors.
Basics: stems, branches and the sixty cycle
Ten stems: Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui. Twelve branches: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai. Paired in order from Jia Zi to Gui Hai they form sixty combinations used cyclically for years, months, days and hours.
Step 1: year pillar
The stem-branch of the birth year — but the year changes at Lichun (around 4 February), not New Year. Someone born on 1 February in a year whose Lichun is 4 February takes the previous year's pillar.
Step 2: month pillar
Month branches are fixed: Lichun to Jingzhe is the Yin month, Jingzhe to Qingming the Mao month, and so on. Months follow solar terms, not lunar month starts.
The month stem follows the year stem by the Five Tigers rule — the Yin month begins at:
- Jia or Ji year: Bing Yin
- Yi or Geng year: Wu Yin
- Bing or Xin year: Geng Yin
- Ding or Ren year: Ren Yin
- Wu or Gui year: Jia Yin
Later months continue in stem order.
Step 3: day pillar
Day stem-branches cycle continuously, unaffected by month length or leap months, so you need an almanac or a known reference date; charting tools compute it. The day stem is the Day Master — you.
Step 4: hour pillar
Hour branches follow double-hours: Zi ≈ 23:00–01:00, Chou 01:00–03:00, etc. The hour stem follows the day stem by the Five Rats rule — the Zi hour begins at:
- Jia or Ji day: Jia Zi
- Yi or Geng day: Bing Zi
- Bing or Xin day: Wu Zi
- Ding or Ren day: Geng Zi
- Wu or Gui day: Ren Zi
Common questions
Which day does 23:00–00:00 belong to?
Some schools move to the next day's pillar; others call it the "late Zi hour", keep the same day and use the next day's Zi-hour stem. Check which rule your tool uses.
Should I use true solar time?
Double-hours were defined by the sun. China's clock time follows 120°E; the farther your birthplace is from that meridian, the bigger the gap. Many practitioners convert to true solar time first.
What about a lunar birthday?
Convert to Gregorian, then apply solar terms. Most tools accept lunar input directly.
Summary
Year by Lichun; month by solar term plus Five Tigers; day from the almanac; hour by double-hour plus Five Rats. The tricky parts are solar-term changes and hour boundaries.
This article is for cultural reference only and is not advice for any decision.