What is the BaZi Four Pillars Calculator?
BaZi ("eight characters") is the classic Chinese system of birth-chart reading. Your birth year, month, day and hour each become a pillar made of a Heavenly Stem (one of ten) on top of an Earthly Branch (one of twelve, the zodiac animals). Together they make eight characters.
Each stem and branch carries one of the five elements (wood, fire, earth, metal, water) in a yin or yang form. The stem of your day pillar is your Day Master: the element that represents you. Everything else is read in relation to it, through the "ten gods".
BaZi uses the solar calendar, not the lunar one: the year begins at Li Chun (around 4 February), and months begin at the solar terms. That is why your BaZi animal can differ from the Chinese New Year animal for January and early February births.
How it works
Year pillar: the year changes when the Sun reaches 315° (Li Chun), found precisely for your birth year. Month pillar: the month branch comes from the Sun's longitude (a new month every 30°, starting at the "jie" solar terms); the month stem follows the classic Five Tigers rule.
Day pillar: from the Julian Day number, (JD + 49) mod 60, checked against known dates (1 January 2000 was a Wu-Wu day; 1 October 1949 a Jia-Zi day). Hour pillar: from local true solar time (longitude correction plus the equation of time), with the day changing at 23:00 (the start of the Rat hour) and the Five Rats rule for the stem.
How it connects to your star sign
The twelve Earthly Branches run parallel to the twelve Western signs: each solar month spans the second half of one sign and the first half of the next. The report shows your Western sun sign alongside your month branch.