How to Calculate a BaZi Chart: The Four Pillars by Hand, One Step at a Time
A BaZi chart is four stem-branch pairs, the year, month, day and hour pillars, eight characters in all. Each has its own method, and none is hard: one division, two short verses and one count of days. Learn them and you will know where every character in a chart comes from.
The four steps at a glance
| Pillar | Based on | How to calculate | The usual mistake |
|---|---|---|---|
| Year | The Start of Spring | (Gregorian year − 4), then the remainder after dividing by 10 and by 12 | Changing the year on January 1 or at Chinese New Year |
| Month | The solar terms (Start of Spring, Awakening of Insects…) | Month branch from the jie term, month stem from the Five Tigers rule | Using the Gregorian or lunar month |
| Day | The date | Count the days from a known date, remainder after dividing by 60 | Forgetting that births after 11 p.m. take the next day |
| Hour | The two-hour period | Hour branch from the period, hour stem from the Five Rats rule | Not taking off daylight saving time; births on an hour boundary |
How we checked: we worked out dates from 1901 to 2099 by the formulas on this page (one day in every 29, all thirteen hours) and compared each chart with our chart engine: 32,565 charts, every one a match. The share of births before the Start of Spring is calculated year by year for 1960–2005.
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).
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).
The two verses
Five Tigers (五虎遁, wu hu dun): from the year stem to the Yin month stem
甲己之年丙作首，乙庚之歲戊為頭，丙辛必定尋庚起，丁壬壬位順行流，更有戊癸何方覓，甲寅之上好追求。
The "tiger" is the Yin (寅) month, the first month of the BaZi year. The verse names the stem that month takes in each kind of year: in a Jia or Ji year the Yin month begins with Bing; Yi or Geng, with Wu; Bing or Xin, with Geng; Ding or Ren, with Ren; Wu or Gui, with Jia.
Five Rats (五鼠遁, wu shu dun): from the day stem to the Zi hour stem
甲己還加甲，乙庚丙作初，丙辛從戊起，丁壬庚子居，戊癸何方發，壬子是真途。
The "rat" is the Zi (子) hour, the first hour of the BaZi day. The verse names the stem that hour takes on each kind of day: on a Jia or Ji day the Zi hour begins with Jia; Yi or Geng, with Bing; Bing or Xin, with Wu; Ding or Ren, with Geng; Wu or Gui, with Ren.
The verses only give the starting point: the Five Tigers give the stem of the Yin month, the Five Rats the stem of the Zi hour. After that, each step along the branches moves the stem one step too. The full lookup tables are on the month pillar and hour pillar pages.
The four most common mistakes
Born in January means the new year has started.
A BaZi year changes at the Start of Spring, which falls between February 3 and 5. Every year about 9.3% of birthdays land between January 1 and the Start of Spring, and they take the previous year's pillar.
The month pillar follows the lunar month.
The month pillar follows the solar terms, not lunar months. Someone born in the first days of the first lunar month may still be in the Chou month.
Born at 11:30 p.m., the day pillar is that day's.
We change the day at 23:00, so a birth after 23:00 takes the next day's pillar. Another school changes the day at midnight; see Early and Late Zi hour.
Use whatever time the birth certificate says.
If you were born under daylight saving time, take off the hour first; the more careful approach also converts to true solar time. See birth time correction.
Read next
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.
Chart calculated? Now read it
The in-depth reading takes your four pillars through the Day Master, the Ten Gods, strength and favorable elements, and writes them up as twelve facets.
How to calculate a BaZi chart: FAQ
How do you calculate a BaZi chart?
Each pillar has its own method. Year: it changes at the Start of Spring; take the remainder of (year − 4). Month: the branch follows the solar terms and the stem comes from the Five Tigers rule. Day: count the days from a known date. Hour: the branch follows the two-hour period and the stem comes from the Five Rats rule.
When does the BaZi year begin?
At the Start of Spring, not on January 1 and not at Chinese New Year. The Start of Spring usually falls on February 3, 4 or 5.
What are the Five Tigers and Five Rats rules?
Two short verses. The Five Tigers (wu hu dun) give the stem of the Yin month from the year stem; the Five Rats (wu shu dun) give the stem of the Zi hour from the day stem. From there, each step along the branches moves the stem one step.
My own calculation doesn't match the website. Why?
The usual causes are the Start of Spring, a solar term boundary, the Late Zi hour day change, or daylight saving time. The tool on this page shows each step so you can see where yours differs.