How to Determine Your Bazi Based on Your Birth Date?

To determine your Bazi (also known as "Four Pillars of Destiny") based on your birth date, you need to sequentially identify the Year Pillar, Month Pillar, Day Pillar, and Hour Pillar. Each pillar consists of one Heavenly Stem (Ten Heavenly Stems: Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui) and one Earthly Branch (Twelve Earthly Branches: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai), forming four pillars and eight characters in total (Bazi).

Here are the detailed steps:

I. Fundamentals of Bazi Astrology

Bazi astrology posits that an individual's birth year, month, day, and hour each correspond to a Stem-Branch combination. These four Stem-Branch combinations collectively form the "Four Pillars," commonly known as "Bazi."

Year Pillar: The Heavenly Stem and Earthly Branch of the birth year.
Month Pillar: The Heavenly Stem and Earthly Branch of the birth month.
Day Pillar: The Heavenly Stem and Earthly Branch of the birth day. The Heavenly Stem of the Day Pillar is called the "Day Master" or "Day Stem," representing the native themselves.
Hour Pillar: The Heavenly Stem and Earthly Branch of the birth hour.

The Heavenly Stems and Earthly Branches follow a fixed cyclic order (the Sixty Jiazi cycle) to record time.

II. Steps and Methods for Constructing Bazi

A. Determining the Year Pillar

The determination of the Year Pillar requires consideration of the Chinese Lunar Calendar (Stem-Branch year notation) and the Solar Terms (Jieqi). In Bazi astrology, the beginning of a year is not January 1st of the Gregorian calendar, nor is it the first day of the Lunar New Year; instead, it is Li Chun (Start of Spring).

Determining the Earthly Branch of the Year (Zodiac Animal)
- The Earthly Branch, or zodiac animal, can be roughly determined based on the Gregorian year.
- Calculation method: The result of (Gregorian year - 4) % 12. 0 corresponds to Zi, 1 to Chou, and so on.
- Key Point: If the birth date is before Li Chun, the year pillar should still be calculated using the Stem-Branch of the previous year. For example, Li Chun in 2024 is on February 4th. If someone was born on February 3rd, 2024, their Year Pillar would still be that of 2023 (Gui Mao), not 2024 (Jia Chen).
Determining the Heavenly Stem of the Year
- This can be determined by the last digit of the Gregorian year.
- Calculation method: The result of (Gregorian year - 4) % 10. 0 corresponds to Jia, 1 to Yi, and so on.
- For example: In 2024, the last digit is 4. (2024 - 4) % 10 = 0, and Jia corresponds to 0. Therefore, the Heavenly Stem for 2024 is Jia.
- Combining with the Earthly Branch, 2024 is the Jia Chen year.

B. Determining the Month Pillar

The determination of the Month Pillar is also based on Solar Terms (Jieqi), not the lunar months. Each Earthly Branch month begins with a specific "Jie" (節, major solar term, not "Qi" 氣, minor solar term).

Determining the Earthly Branch of the Month
- The twelve Earthly Branches correspond to twelve months, but these refer to Solar Term months, not lunar months.
- | Earthly Branch | Solar Term Month | Approximate Gregorian Date Range |\n | :--- | :----- | :----------------- |\n | Yin | First Month | Li Chun (Feb 4-5) to Jing Zhe |\n | Mao | Second Month | Jing Zhe (Mar 5-6) to Qing Ming |\n | Chen | Third Month | Qing Ming (Apr 4-5) to Li Xia |\n | Si | Fourth Month | Li Xia (May 5-6) to Mang Zhong |\n | Wu | Fifth Month | Mang Zhong (Jun 5-6) to Xiao Shu |\n | Wei | Sixth Month | Xiao Shu (Jul 6-7) to Li Qiu |\n | Shen | Seventh Month | Li Qiu (Aug 7-8) to Bai Lu |\n | You | Eighth Month | Bai Lu (Sep 7-8) to Han Lu |\n | Xu | Ninth Month | Han Lu (Oct 8-9) to Li Dong |\n | Hai | Tenth Month | Li Dong (Nov 7-8) to Da Xue |\n | Zi | Eleventh Month | Da Xue (Dec 6-7) to Xiao Han |\n | Chou | Twelfth Month | Xiao Han (Jan 5-6) to Li Chun |
- Key Point: You must use a perpetual calendar to check the exact transition time of Solar Terms for the specific year, down to the minute, as the birth date might fall precisely at a transition point between two Solar Terms. For example, if someone is born an hour before Jing Zhe, their Month Pillar still belongs to the Yin month. Leap months have no impact on the Month Pillar in Bazi plotting, as Bazi uses a solar calendar system.
Determining the Heavenly Stem of the Month
- The Heavenly Stem of the month is determined by the Year Stem and the Month Branch using the "Five Tiger Escaping Formula" (五虎遁歌诀).
- Formula:\n * For Jia or Ji years, Bing starts in the First (Yin) month. (甲己之年丙作首)\n * For Yi or Geng years, Wu starts in the First (Yin) month. (乙庚之岁戊为头)\n * For Bing or Xin years, Geng starts in the First (Yin) month. (丙辛之岁寻庚上)\n * For Ding or Ren years, Ren starts in the First (Yin) month. (丁壬壬位顺水流)\n * For Wu or Gui years, Jia starts in the First (Yin) month. (戊癸之年甲寅居)
- Once the Heavenly Stem for the Yin month is determined, the Heavenly Stems for subsequent months follow the sequence of Heavenly Stems. For example, if the Heavenly Stem for Yin month is Bing, then the Heavenly Stem for Mao month is Ding, for Chen month is Wu, and so on.

C. Determining the Day Pillar

The Day Pillar is the most crucial part of Bazi plotting and the only one that cannot be derived by simple calculation; it must be looked up in a perpetual calendar.

Using a Perpetual Calendar
- The Day Pillar follows the Sixty Jiazi Stem-Branch cycle, with each day corresponding to a fixed Stem-Branch combination, independent of the year and month.
- You need to look up the Stem-Branch corresponding to your birth date (Gregorian or lunar) in a perpetual calendar. For example, April 20, 2024 (Gregorian) is Jia Chen year, Wu Chen month, Geng Yin day.
Importance of the Day Master (Day Stem)
- The Heavenly Stem of the Day Pillar is the center of the Bazi chart, representing the native themselves (e.g., "Geng" in "Geng Yin day" is the Day Master). When analyzing a Bazi chart, all other Stems and Branches are interpreted in relation to the Day Master.

D. Determining the Hour Pillar

The determination of the Hour Pillar requires the birth hour and the Heavenly Stem of the Day Pillar.

Determining the Earthly Branch of the Hour
- A day has twelve two-hour segments, each corresponding to an Earthly Branch.
- | Earthly Branch | Time (24-hour format) |\n | :--- | :------------- |\n | Zi | 23:00 - 00:59 |\n | Chou | 01:00 - 02:59 |\n | Yin | 03:00 - 04:59 |\n | Mao | 05:00 - 06:59 |\n | Chen | 07:00 - 08:59 |\n | Si | 09:00 - 10:59 |\n | Wu | 11:00 - 12:59 |\n | Wei | 13:00 - 14:59 |\n | Shen | 15:00 - 16:59 |\n | You | 17:00 - 18:59 |\n | Xu | 19:00 - 20:59 |\n | Hai | 21:00 - 22:59 |
- Key Point: You need to use True Solar Time. The longitude of the birthplace, time zone, and Daylight Saving Time can all affect the accuracy of the hour. Taking Beijing Time (UTC+8) as an example, if the birthplace is west of the UTC+8 zone, its local time will be later than Beijing Time; conversely, it will be earlier. Typically, the local Gregorian time at the birthplace needs to be converted to True Solar Time to determine the Hour Pillar.
Determining the Heavenly Stem of the Hour
- The Heavenly Stem of the hour is determined by the Day Stem and the Hour Branch using the "Five Rat Escaping Formula" (五鼠遁歌诀).
- Formula:\n * For Jia or Ji days, Jia starts in the Zi hour. (甲己还加甲)\n * For Yi or Geng days, Bing starts in the Zi hour. (乙庚丙作初)\n * For Bing or Xin days, Wu starts in the Zi hour. (丙辛从戊起)\n * For Ding or Ren days, Geng starts in the Zi hour. (丁壬庚子居)\n * For Wu or Gui days, Ren starts in the Zi hour. (戊癸何方发，壬子是真途)
- Once the Heavenly Stem for the Zi hour is determined, the Heavenly Stems for subsequent hours follow the sequence of Heavenly Stems. For example, if the Heavenly Stem for Zi hour is Jia, then the Heavenly Stem for Chou hour is Yi, for Yin hour is Bing, and so on.

III. Summary and Important Notes

Precise Birth Time: The hour is a two-hour interval. If the birth time is at an hour boundary, even a minute's difference can lead to a completely different Hour Pillar, significantly impacting the Bazi chart.
True Solar Time: When plotting the Hour Pillar, the standard time at the birthplace (usually local time zone time) must be converted to True Solar Time.
- Calculation Formula: True Solar Time = Local Standard Time + (Local Longitude - 120) / 15 + Equation of Time (the Equation of Time usually varies little, but should be considered for precise calculations).
- If Daylight Saving Time was in effect, first subtract the time added for DST.
Importance of Perpetual Calendar: For determining the Day Pillar and the precise Solar Term transition points for the Year and Month Pillars, a perpetual calendar is an indispensable tool.
Avoid Misconceptions about Zodiac Years: People sometimes mistakenly believe that the Lunar New Year (Spring Festival) marks the beginning of a zodiac year. However, in Bazi astrology, the point of change for the zodiac animal (Earthly Branch) is Li Chun.
Online Bazi Plotting Tools: Due to the complexity and potential for error in manually calculating True Solar Time, looking up Solar Terms, and finding Stem-Branches for the Day Pillar, it is highly recommended to use professional online Bazi plotting tools. These tools typically require input of the birthplace and specific birth time down to the minute, and can automatically perform True Solar Time and Solar Term conversions, directly providing the Four Pillars of Destiny. Nevertheless, understanding the underlying principles is still beneficial.

By following the steps above, you can accurately determine your Bazi based on your birth date (year, month, day, hour).