How a Four Pillars Chart Is Built: Stems, Branches and the Sixty-Year Cycle

A Saju chart looks mysterious at first: eight Chinese characters arranged in four columns. But the logic behind it is entirely calendrical. Once you understand the two sets of symbols and the cycle that combines them, you can read the skeleton of any chart at a glance.

The ten Heavenly Stems

The Heavenly Stems (천간, cheongan) are ten symbols that express the Five Elements in their Yang and Yin forms. Yang is the outward, expanding, active expression of an element; Yin is the inward, receptive, refined expression.

• 甲 Jia (Gap): Yang Wood, the tall tree
• 乙 Yi (Eul): Yin Wood, the flowering vine
• 丙 Bing (Byeong): Yang Fire, the sun
• 丁 Ding (Jeong): Yin Fire, the candle flame
• 戊 Wu (Mu): Yang Earth, the mountain
• 己 Ji (Gi): Yin Earth, the fertile field
• 庚 Geng (Gyeong): Yang Metal, the sword or raw ore
• 辛 Xin (Sin): Yin Metal, the polished jewel
• 壬 Ren (Im): Yang Water, the ocean or great river
• 癸 Gui (Gye): Yin Water, rain and dew

The twelve Earthly Branches

The Earthly Branches (지지, jiji) are the twelve symbols most people know through the zodiac animals. Each branch also carries an element and marks a month of the solar year and a two-hour block of the day.

子 Rat (Water), 丑 Ox (Earth), 寅 Tiger (Wood), 卯 Rabbit (Wood), 辰 Dragon (Earth), 巳 Snake (Fire), 午 Horse (Fire), 未 Goat (Earth), 申 Monkey (Metal), 酉 Rooster (Metal), 戌 Dog (Earth) and 亥 Pig (Water). Notice how the branches trace the seasons: two Wood branches for spring, two Fire branches for summer, two Metal branches for autumn, two Water branches for winter, and an Earth branch at each change of season.

The sixty-step cycle

Stems and branches are paired in order: the first stem with the first branch (甲子), the second with the second (乙丑), and so on. Because there are ten stems and twelve branches, the pairs only line up again after sixty steps. This sixty-step cycle, often called the sexagenary cycle, is the heartbeat of the traditional calendar. A person's sixtieth birthday, hwangap (환갑) in Korean, is celebrated precisely because it is the year the cycle returns to the pair they were born in.

Only half of all possible stem-branch combinations ever occur: Yang stems always pair with Yang branches and Yin stems with Yin branches. That is why there are sixty pillars rather than a hundred and twenty.

Building each pillar

Each of the four pillars is simply the position of one unit of time in the sixty-cycle:

• Year pillar: the year advances one step through the cycle each year. In Saju the year begins at Ipchun (입춘), the start of spring, around February 4. Someone born on January 20 belongs to the previous Saju year, even though the Gregorian year has already changed.
• Month pillar: months follow the solar terms rather than the moon. The Tiger month begins at Ipchun, the Rabbit month around March 6, and so on, each lasting roughly thirty days. The month's stem follows from the year's stem by a fixed rule.
• Day pillar: days run through the sixty-cycle continuously, without any reset for months or years. For example, January 1, 2000 was a 戊午 (Yang Earth Horse) day, and every day since has advanced one step from there.
• Hour pillar: the day is divided into twelve two-hour blocks, starting with the Rat hour from 11 p.m. to 1 a.m. The hour's stem follows from the day's stem.

Why the birth time matters, and what if you don't know it

The hour pillar adds two of the eight characters, so it can change the element balance noticeably and, in traditional practice, it says something about your later life and your children. If you do not know your birth time, the chart is read from six characters instead of eight. The Day Master, which is the heart of the reading, comes from the day pillar and does not depend on the time at all, so a six-character reading is still meaningful.

Births close to a boundary deserve a little caution. If you were born within a day or so of a solar term, your month pillar may differ between calculators that use exact astronomical times and those that use approximate dates. Likewise, a birth right at the edge of a two-hour block can fall on either side depending on whether local clock time or true solar time is used.

How Cosmic Saju calculates your chart

Cosmic Saju calculates pillars from your local birth date and time. It uses approximate solar-term dates to decide where months begin and does not apply a true-solar-time correction for your longitude. For most people this gives the same chart as a professional calculation. If you were born near a solar term or right at an hour boundary, treat the reading as one of two possible charts and compare it with a specialist's calculation if you want certainty.

Once the four pillars are in place, the interesting work begins: identifying your Day Master, weighing the Five Elements and following how the decades of your Great Luck Cycles move through the chart.