The short version
Think of a birth chart built from the calendar rather than the sky. Western astrology looks at where the planets were when you were born. Saju looks at which date it was in a sixty step cycle of years, months, days and hours that East Asia has counted for more than two thousand years.
Each of the four time units (year, month, day, hour) is written as a pair of characters: a heavenly stem on top and an earthly branch below. Four pairs make eight characters, which is why Koreans often say 사주팔자 saju palja, four pillars and eight characters. In everyday Korean, palja on its own has come to mean fate, as in the phrase that someone's palja is good.
Every one of those eight characters belongs to one of five elements: wood, fire, earth, metal and water. The reading comes from how the elements balance and how they relate to one character in particular, the stem of your day pillar, which stands for you.
Stems and branches
There are ten heavenly stems (천간 cheongan): 甲 乙 丙 丁 戊 己 庚 辛 壬 癸. They are the five elements, each in a yang (active, outward) and a yin (receptive, inward) form. So 甲 Gap is yang wood, a tall tree, and 乙 Eul is yin wood, a vine or flower.
There are twelve earthly branches (지지 jiji): 子 丑 寅 卯 辰 巳 午 未 申 酉 戌 亥. You already know them as the twelve animals, from the Rat to the Pig. Each branch also has an element, a season, a two hour block of the day, and a few stems hidden inside it (지장간 jijanggan).
Stems and branches pair up in order, 甲子, 乙丑, 丙寅 and so on, and because ten and twelve only line up every sixty steps, the cycle is sixty long. The same sixty pairs name years, months, days and hours. 2026, for example, is 丙午 Byeong-o: yang fire over the horse, which is why Koreans call it the year of the red horse.
The day master is you
Of the eight characters, one matters most: the stem of the day pillar, called the day master (일간 ilgan). It is read as the self. If your day master is 丙, you are read as the sun. If it is 癸, you are rain.
Every other character is read by its relationship to that day master. Does it feed you, drain you, control you, or share your element? Those relationships have names, the ten gods (십신 sipsin), and they are how a Saju reader talks about friends, work, structure, learning and self expression.
How it differs from what you may know
Your Chinese zodiac animal is only one of the eight characters in Saju: the branch of your year pillar. Two people born in the same year share it, which is why Saju goes further and looks at the month, day and hour too. The day pillar alone changes every day, so it is far more personal.
Saju's calendar is solar, even though people often call it the lunar calendar. The year starts at Ipchun (입춘, the start of spring), when the Sun reaches 315 degrees along its path, around 4 February. It does not start on 1 January, and it does not start at the lunar new year. The months start at the solar terms (절기 jeolgi) too, so someone born on 3 February usually belongs to the previous year's animal.
Compared with Western astrology, there are no planets, houses or aspects. The two systems grew up separately and answer different questions. Many people enjoy both.
Where it comes from
The stem and branch calendar is ancient Chinese in origin, and the method of reading a chart from the year, month, day and hour took shape in China over many centuries, where it is called BaZi (八字, eight characters). It reached Korea long ago and developed its own practice, vocabulary and habits, from Korean terms such as 궁합 gunghap for compatibility to the Korean attention to 원진 wonjin, the resentment pairs.
In Korea today Saju sits comfortably in everyday life. People visit saju cafes with friends, check their 신년운세 sinnyeon unse (the reading for the new year) around the solar new year, and some families still look at gunghap before a wedding. Most people treat it the way many Westerners treat their horoscope: part tradition, part conversation starter, part mirror.
What this site does
The calculator works out your four pillars from your birth date, time and place. It finds the solar terms from the Sun's position, counts the day in the sixty day cycle, and can correct your birth time to local solar time, including Korea's historical clock changes. Then it shows the day master, the element balance, the ten gods and your ten year luck pillars, all in Hanja, Hangul and English.
Everything here is for entertainment and self reflection. A chart can give you words for your temperament and some questions worth asking. It cannot tell you what will happen, and it is no substitute for advice from a qualified person about health, money or law.
Questions
Do I need my birth time?
No. Without a time you get three pillars (year, month and day) and the day master, which is the heart of the reading. The hour pillar adds two more characters.
Is Saju the same as Chinese BaZi?
They share the same calendar and core method. Korean practice has its own vocabulary, emphases and customs, such as gunghap before marriage and attention to wonjin pairs.
Why is my animal different from what I expected?
Because the Saju year starts at Ipchun, around 4 February. If you were born in January or early February, your year pillar is usually the previous year's animal.
Is it a prediction?
Not here. We present Saju as a traditional way of describing temperament and timing, for entertainment and reflection only.