*Note: This calculator uses algorithmic approximations for solar terms. For precise astrological readings, exact longitude and solar time correction are required.
Understanding the Python Bazi Four Pillars Calculation
The Bazi (八字), or "Four Pillars of Destiny," is a sophisticated Chinese astrological system that maps a person's birth year, month, day, and hour onto a 60-year cyclical calendar known as the Gan-Zhi (stem-branch) system. Traditionally, determining these pillars required complex almanacs to identify precise solar terms (Jie Qi).
In modern applications, a "Python Bazi calculation" refers to using computational algorithms to determine these pillars mathematically, rather than manual lookup. This approach involves modular arithmetic and precise day-counting functions to align the Gregorian calendar with the Chinese sexagenary cycle.
The Algorithmic Logic
The calculation rests on connecting time components to the 10 Heavenly Stems (e.g., Jia, Yi, Bing) and 12 Earthly Branches (e.g., Zi/Rat, Chou/Ox).
Year Pillar: This is the simplest calculation. It uses a reference year (e.g., 1924 was the start of a cycle, Jia-Zi) and applies modulo 60 arithmetic to find the current year's position in the cycle.
Day Pillar: This is computationally intensive. It requires calculating the exact number of days elapsed since a reference base date (like January 1, 1900) and applying modulo 60 to that total count to determine the day's Stem and Branch combo.
Month and Hour Pillars: These are derived based on rules related to the Year and Day stems respectively. For example, the "Five Tigers Searching" rule determines the Month Stem based on the Year Stem, and the "Five Rats Searching" rule determines the Hour Stem based on the Day Stem.
Example Calculation Scenario
Consider a birth date of May 15, 1990, at 14:00 (2 PM). An algorithmic calculator processes this data:
Year (1990): The algorithm calculates the offset from the base cycle, resulting in a Year Pillar of Geng-Wu (Yang Metal Horse).
Day (May 15, 1990): By counting total days from a base point, the Day Pillar is determined to be Bing-Xu (Yang Fire Dog).
Month (May): Based on the Year Stem (Geng) and the solar month approximation for May, the Month Pillar is calculated as Xin-Si (Yin Metal Snake).
Hour (14:00): 14:00 falls in the Wei time slice (13:00-15:00). Based on the Day Stem (Bing), the Hour Pillar is calculated as Yi-Wei (Yin Wood Goat).
This computational approach allows for rapid generation of Bazi charts, forming the basis for computerized astrological analysis.
var stems = [
"Jia (Yang Wood)", "Yi (Yin Wood)", "Bing (Yang Fire)", "Ding (Yin Fire)",
"Wu (Yang Earth)", "Ji (Yin Earth)", "Geng (Yang Metal)", "Xin (Yin Metal)",
"Ren (Yang Water)", "Gui (Yin Water)"
];
var branches = [
"Zi (Rat)", "Chou (Ox)", "Yin (Tiger)", "Mao (Rabbit)",
"Chen (Dragon)", "Si (Snake)", "Wu (Horse)", "Wei (Goat)",
"Shen (Monkey)", "You (Rooster)", "Xu (Dog)", "Hai (Pig)"
];
function calculateBazi() {
var yStr = document.getElementById("birthYear").value;
var mStr = document.getElementById("birthMonth").value;
var dStr = document.getElementById("birthDay").value;
var hStr = document.getElementById("birthHour").value;
var errorDiv = document.getElementById("errorMessage");
var resultDiv = document.getElementById("result");
errorDiv.style.display = "none";
errorDiv.innerHTML = "";
resultDiv.style.display = "none";
var y = parseInt(yStr);
var m = parseInt(mStr);
var d = parseInt(dStr);
var h = parseInt(hStr);
if (isNaN(y) || isNaN(m) || isNaN(d) || isNaN(h) || y 2100 || m 12 || d 31 || h 23) {
errorDiv.innerHTML = "Please enter valid numeric values for Year (1901-2100), Month (1-12), Day (1-31), and Hour (0-23).";
errorDiv.style.display = "block";
return;
}
// 1. Year Pillar Calculation
// Base: 1924 was Jia(0) Zi(0).
var baseYear = 1924;
var yearOffset = y – baseYear;
// Handle negative offsets for years before base
while (yearOffset 1, Feb->2, …, Dec->12(0).
var mBranchIdx = m % 12;
// Month Stem: "Five Tigers Searching" rule based on Year Stem.
// Year Stem indices: Jia(0)/Ji(5) -> Start Bing(2) for Feb(Tiger/2) month.
// Yi(1)/Geng(6) -> Start Wu(4)
// Bing(2)/Xin(7) -> Start Geng(6)
// Ding(3)/Ren(8) -> Start Ren(8)
// Wu(4)/Gui(9) -> Start Jia(0)
var mStemBase = (yStemIdx % 5) * 2 + 2;
// Adjust base stem for the specific month branch.
// The base is for Tiger month (index 2). We need offset from index 2.
// We must handle circular array math carefully.
// Shift branch index so Tiger is 0 for calculation: (mBranchIdx + 10) % 12
var monthOffsetFromTiger = (mBranchIdx + 10) % 12;
var mStemIdx = (mStemBase + monthOffsetFromTiger) % 10;
// 3. Day Pillar Calculation (Continuous Day Count)
// Base Reference: Jan 1, 1900 was Jia(0)-Xu(10).
var totalDays = 0;
for (var i = 1900; i < y; i++) {
totalDays += (i % 4 === 0 && (i % 100 !== 0 || i % 400 === 0)) ? 366 : 365;
}
var daysInMonth = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
// Leap year check for current year
if (y % 4 === 0 && (y % 100 !== 0 || y % 400 === 0)) { daysInMonth[2] = 29; }
for (var j = 1; j Start Hour Zi is Jia(0)
// Yi(1)/Geng(6) -> Start Hour Zi is Bing(2)
// Bing(2)/Xin(7) -> Start Hour Zi is Wu(4)
// Ding(3)/Ren(8) -> Start Hour Zi is Geng(6)
// Wu(4)/Gui(9) -> Start Hour Zi is Ren(8)
var hStemBase = (dStemIdx % 5) * 2;
var hStemIdx = (hStemBase + hBranchIdx) % 10;
// Display Results
document.getElementById("yearStem").innerText = stems[yStemIdx];
document.getElementById("yearBranch").innerText = branches[yBranchIdx];
document.getElementById("monthStem").innerText = stems[mStemIdx];
document.getElementById("monthBranch").innerText = branches[mBranchIdx];
document.getElementById("dayStem").innerText = stems[dStemIdx];
document.getElementById("dayBranch").innerText = branches[dBranchIdx];
document.getElementById("hourStem").innerText = stems[hStemIdx];
document.getElementById("hourBranch").innerText = branches[hBranchIdx];
resultDiv.style.display = "block";
}