Luck Pillars (大運): how they are calculated

A BaZi chart is a snapshot of one moment, but the tradition also describes change over time. Its main tool for that is the Luck Pillars (大運): a sequence of stem-branch pairs, each covering ten years, which readers set beside the birth chart to talk about the emphasis of different stages of life. On top of them, each calendar year brings its own pillar, the flow year (流年).

All of it is calculated from the birth chart and the solar calendar. Here is how.

Step 1: forward or backward

The direction depends on the year stem and on recorded sex, following the traditional rule:

• Forward (順) for a man born in a yang year (stems 甲 丙 戊 庚 壬) or a woman born in a yin year (乙 丁 己 辛 癸).
• Backward (逆) for a man born in a yin year or a woman born in a yang year.

The year stem is that of the BaZi year, which begins at the Start of Spring (立春), not on 1 January. The traditional rule needs one sex or the other, so if none is given our calculator uses the yang-year-forward (male) convention and says so on the chart.

Step 2: the sequence

Luck pillars grow out of the month pillar. Going forward, the first luck pillar is the pair that follows the month pillar in the sixty-cycle; going backward, it is the pair before it. Each later pillar takes one more step the same way.

With a month pillar of 辛巳, the forward sequence is 壬午, 癸未, 甲申 and so on; the backward sequence is 庚辰, 己卯, 戊寅, 丁丑. Our chart lists ten pillars, which covers roughly a century.

Step 3: when the first one starts

The start age comes from the distance between the birth and the nearest month boundary:

• going forward, count from the birth to the next 節;
• going backward, count back from the birth to the previous 節.

The 節 (jié) are the twelve solar terms that open the BaZi months: 立春, 驚蟄, 清明, 立夏, 芒種, 小暑, 立秋, 白露, 寒露, 立冬, 大雪 and 小寒. The other twelve solar terms, the 中氣, play no part here.

The classical conversion is three days for one year. It follows that one day stands for four months and one two-hour period (時辰) for ten days. Our calculator measures the interval to the minute and keeps the same ratio: 4,320 minutes make a year, 360 minutes a month and 12 minutes a day. That span is added to the birth moment to give the date the first luck pillar begins, and each later pillar begins exactly ten years after the one before.

Some references count whole days and two-hour periods instead of minutes, which can move the start by days or weeks. Schools differ; the chart always shows the exact date it used.

A worked example

Take a woman born on 15 May 1990 at 10:30 in Shanghai. Her year is 庚午, and 庚 is yang, so for a woman the pillars run backward. Her month pillar, 辛巳, began at 立夏 on 6 May 1990 at 02:35 Beijing time, about nine days and eight hours before the birth. Divided by three, that is a little over three years: her first luck pillar, 庚辰, begins at about 3, followed by 己卯 at about 13, 戊寅 at about 23, and so on.

Why references disagree about the age

The site gives the start in completed years at the start date ("age 3.1"). Many Chinese almanacs print the nominal age (虛歲), which counts the year of birth as 1, so the same pillar may be listed as starting at 4. Both describe the same date.

Solar terms are single astronomical instants, so the start is measured from the birth instant, not from local clock time. True solar time can change the hour pillar, but it does not change when the luck pillars begin.

Before the first pillar

The years between birth and the first luck pillar have no luck pillar of their own. Traditions read that stretch in different ways (some use a separate "minor luck", 小運); our chart simply starts its list at the first luck pillar.

Flow years (流年)

Every year also has a stem-branch pair, and in BaZi it changes at the Start of Spring: 2026 is 丙午, 2027 is 丁未, 2028 is 戊申, 2029 is 己酉. The chart page lists the current year and the next three. For each it gives the Ten Gods relative to your Day Master (one for the stem, one for the branch through its main hidden stem) and any interactions with your birth pillars: clashes, combinations, or a year that repeats one of your pillars exactly (伏吟).

How readers use them

A luck pillar is read like a season. Its elements are compared with the ones the chart favours, and its Ten Gods suggest which themes are louder for a decade. A flow year adds a shorter rhythm on top. Neither is a forecast of events, and none of it settles how your life goes.

Code first, words second

Direction, start date and every pillar are computed in code from your birth data and the solar-term tables, and they appear on the chart before any text is written. The AI is given the finished list to describe; it cannot add, move or alter a pillar.