The BaZi Day Pillar: Start From a Day You Know and Count
The stem of the day pillar is the Day Master, the center of the whole chart. It is worked out differently from the other three pillars: the day's stem-branch pair moves one step every day and repeats every sixty days, with no alignment to months or years. So you start from a day you know and count.
The method
- Pick a reference date. We use January 1, 2000, a Wu-Wu (戊午) day, number 55 in the sixty Jiazi (index 54, counting from 0).
- Count the days between the birth date and the reference date: positive if after, negative if before.
- Take (54 + the difference) divided by 60 and keep the remainder (if it is negative, add 60). Look it up in the table below: that is the day pillar.
- If the birth was after 11 p.m., we change the day at 23:00, so use the next day.
The sixty Jiazi in order (index from 0)
| Index | +0 | +1 | +2 | +3 | +4 | +5 | +6 | +7 | +8 | +9 |
|---|---|---|---|---|---|---|---|---|---|---|
| 0–9 | 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 |
| 10–19 | 甲戌 Jia-Xu | 乙亥 Yi-Hai | 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 |
| 20–29 | 甲申 Jia-Shen | 乙酉 Yi-You | 丙戌 Bing-Xu | 丁亥 Ding-Hai | 戊子 Wu-Zi | 己丑 Ji-Chou | 庚寅 Geng-Yin | 辛卯 Xin-Mao | 壬辰 Ren-Chen | 癸巳 Gui-Si |
| 30–39 | 甲午 Jia-Wu | 乙未 Yi-Wei | 丙申 Bing-Shen | 丁酉 Ding-You | 戊戌 Wu-Xu | 己亥 Ji-Hai | 庚子 Geng-Zi | 辛丑 Xin-Chou | 壬寅 Ren-Yin | 癸卯 Gui-Mao |
| 40–49 | 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 | 壬子 Ren-Zi | 癸丑 Gui-Chou |
| 50–59 | 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 |
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).
Why there is no simple formula
A year has 365 or 366 days, not a multiple of 60, so the same calendar date has a different day pillar every year. When calculating by hand, the error-prone part is counting the days (leap years, months of different lengths); in practice most people look it up in a perpetual calendar or use a tool. Our day pillars come from the open-source calendar library lunar-javascript, and the method on this page matches it chart for chart.
Watch out for the Late Zi hour
For the Late Zi hour, 23:00–23:59, we use the next day's pillar; another school changes the day only after midnight. The two give different Day Masters; see Early and Late Zi 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 day pillar
Enter your birthday, and the tool shows the number of days from the reference date and works out your day pillar and Day Master step by step.
Day pillar FAQ
How do you calculate the BaZi day pillar?
Count from a date whose stem-branch pair you know. Taking January 1, 2000, Wu-Wu (index 54), as the reference, (54 + the difference in days) divided by 60 leaves the index; look it up in the sixty Jiazi.
Why is the day pillar different for the same date every year?
The day cycle repeats every sixty days, and a year of 365 or 366 days is not a multiple of 60, so the same calendar date lands on a different pillar each year.
Born at 11 p.m.: which day is my day pillar?
We change the day at 23:00, so the day pillar is the next day's. Another school changes it at midnight, and the two give different Day Masters.