TL;DR: In Bazi, the Dayun (major luck cycles) are ten-year periods that follow the start of luck. The direction, forward or backward, is determined by gender combined with the yin-yang of the year stem: yang males and yin females go forward, yin males and yang females go backward, following the order of the Sixty Jiazi. The age of starting luck is calculated from the distance between the birth date and the nearest solar term, with the convention that three days equal one year, one day equals four months, and one two-hour period equals ten days. Interpreting a Dayun cannot be separated from the original chart: one must place the Dayun's stem and branch alongside the chart's useful god and favorable/unfavorable elements, and then examine the annual pillars superimposed. Different schools also differ on whether the Dayun's stem or branch is more important, on how to round the starting age, and on whether to use the minor luck cycles. The original text of Zi Ping Zhen Quan examines the Dayun stem character by character, while Xu Lenwu's commentary examines it by the direction of the branch.
What Is a BaZi Major Cycle and How Does It Differ from the Original Chart?
The major cycle is a series of consecutive ten-year periods in a BaZi (Four Pillars) chart, each step being a new pair of stem and branch derived by the chart-maker from the month pillar, not something already present in the four original pillars. The four pillars of year, month, day and hour together form eight characters called the original chart, which describes the underlying structure of the chart, while the major cycle is the layer of time running through that structure, changing once every ten years. According to Ho Peng Yoke (2003), Chinese Mathematical Astrology: Reaching Out to the Stars, RoutledgeCurzon, the BaZi system in general uses the stems and branches of the year, month, day and hour of birth as its raw material, in which the stem of the day pillar is called the Day Master or Day Stem, serving as the reference point for all the remaining factors. The major cycle does not change that reference point, it only brings new stems and branches onto the table and forces the interpreter to read how the original chart responds to those stems and branches.
A clear distinction must be made with the major cycle in Tử Vi (Vietnamese astrology). The Tử Vi major cycle is divided according to the chart's bureau number, each of the twelve palaces taking charge of a ten-year period, and one reads the Tử Vi major cycle by moving the Life palace, the Wealth palace, the Career palace and the Fortune palace to their new positions. The BaZi major cycle has no palaces and no bureau number, it is a linear sequence of stems and branches, so the two share the term "major cycle" but the nature of the data is entirely different.
Why Does the Major Cycle Run Forward or Backward?
The direction of the major cycle is decided by two factors at once: the gender of the person whose chart is being cast and the yin-yang of the birth year stem. According to Vạn Dân Anh (Ming dynasty), Tam Mệnh Thông Hội, volume 2: On Reckoning the Month and Hour and On the Major Cycle, the convention is that yang males and yin females run forward, yin males and yang females run backward, following the order of the Sixty Jiazi. In other words, one does not choose the direction oneself; the direction is fixed right from the year stem and the gender, after which one simply steps forward or backward from the month pillar.
A concrete example makes this easier to picture. A person born in a Giáp Tý year, with the birth month being the Đinh Sửu pillar. The year stem Giáp is yang. If male, that is a yang male, the cycle runs forward: Mậu Dần, Kỷ Mão, Canh Thìn...; if it is also a Giáp Tý year with a Đinh Sửu month but the person is female, that is a yang female, the cycle runs backward: Bính Tý, Ất Hợi, Giáp Tuất... The direction is not a formality; it determines the entire sequence of stems and branches that person will pass through in life, so getting even one of the two input facts wrong makes the whole cycle table wrong.
It should also be said plainly that this is a convention, not an empirically verifiable truth. Among BaZi researchers, this convention is accepted for the consistency of the system, but there is no way to verify by experiment that a yang male must necessarily run forward.
How Is the Starting Age of the Cycle Calculated from the Number of Days to the Nearest Solar Term?
The starting age of the cycle is the number of years, months and days from the moment of birth to the moment the first major cycle takes effect. The chart-maker counts the distance from the date and hour of birth to the nearest solar term in the direction the cycle runs: if the cycle runs forward, one counts to the solar term ahead; if the cycle runs backward, one counts back to the solar term behind. Once the number of days is known, it is converted at the ratio of three days to one year, one day to four months, and one canh giờ (two hours) to ten days, then added to the birth date to give the starting point of the cycle. This convention is recorded in Vạn Dân Anh (Ming dynasty), Tam Mệnh Thông Hội, volume 2: On Reckoning the Month and Hour and On the Major Cycle.
For example, if the distance to the solar term is fifteen days and the cycle runs forward, then fifteen divided by three gives five years, meaning the first major cycle begins when the person is about five years old. If the distance is sixteen days, then the first fifteen days convert to five years and the remaining odd day converts to four months, giving a starting point of five years and four months. This ratio of three days to a year is the central convention of the method of establishing the major cycle, and it is also the place where mistakes are most likely if the chart-maker works by hand without cross-checking the solar terms.
Why three days? The common explanation is to take the rhythm of the solar terms as nature's measure of time, then map that rhythm onto the time of a human life. A year has about three hundred and sixty-five days, and a full round of solar terms also closes within about that span, so one day in the distance to the solar term is regarded as corresponding to one third of a year of age. This is the reasoning of the system, not a physical measurement, and the various schools still make adjustments around this figure.
Can a Major Cycle Table Be Built with the Calculation Core?
One should not calculate by hand. The existing BaZi calculation core, for example LapBatTu together with solar term data, only produces the four pillars and background information, and has no major cycle function. To get a correct major cycle table, one must add a function that takes as input the four established pillars, the gender and the solar term table, and returns the direction, the starting point of the cycle and the sequence of stems and branches of the eight major cycles. Adding the function is a technical necessity, not an option, because hand calculation easily goes wrong in three places: determining the nearest solar term, converting odd days into months, and stepping the stems and branches in the correct direction.
Below is the table of eight major cycles for a sample chart, built with the calculation core after the major cycle function was added. The sample chart uses a male born in a Giáp Tý year, Đinh Sửu month; the hour is not given so as to focus on the cycle section. Because he is a yang male the cycle runs forward, and assuming the distance to the solar term is fifteen days, the starting point is about five years of age. The table has been checked by the calculation core.
| Major cycle | Stem and branch | Age range | Stem of the cycle | Branch of the cycle |
|---|---|---|---|---|
| 1 | Mậu Dần | 5 to 15 | Mậu | Dần |
| 2 | Kỷ Mão | 15 to 25 | Kỷ | Mão |
| 3 | Canh Thìn | 25 to 35 | Canh | Thìn |
| 4 | Tân Tỵ | 35 to 45 | Tân | Tỵ |
| 5 | Nhâm Ngọ | 45 to 55 | Nhâm | Ngọ |
| 6 | Quý Mùi | 55 to 65 | Quý | Mùi |
| 7 | Giáp Thân | 65 to 75 | Giáp | Thân |
| 8 | Ất Dậu | 75 to 85 | Ất | Dậu |
This table is only a framework of stems and branches and a framework of ages. It says nothing yet about fortune or misfortune, because to know fortune or misfortune one must place each pair of stem and branch in relation to the original chart and to the chart's useful god.
How Does One Read a Ten-Year Major Cycle Against the Useful God?
Reading a major cycle means comparing the stems and branches of the cycle with the favorable and unfavorable elements of the original chart, not looking up a ready-made table of good and bad. First one must determine the useful god and the unfavorable god of the chart, that is, which element benefits and which element harms the Day Master within that specific structure. How to determine the useful god has been discussed in a separate article on the useful god, and how to measure the strength or weakness of the Day Master has been discussed in the article on strength and weakness; here only the conclusions are reused, without repeating the reasoning.
Once the favorable and unfavorable elements are known, the principle of reading is fairly straightforward: if the stem and branch of the cycle fall into a favorable element, that period is smoother; if they fall into an unfavorable element, that period is harder; and the degree still depends on whether those stems and branches are combined, clashed, or struck by the original chart. A major cycle whose stem is a favorable element but whose branch is an unfavorable element will not read the same as one where both stem and branch are favorable. This is also why the question of whether the stem or the branch carries more weight matters so much.
On this point the schools do not agree, and the reader should know which convention they are following. The original text of Tử Bình Chân Thuyên (chapter On the Movement of Cycles) says to match the stem of the cycle with the favorable and unfavorable elements of the chart, examining each character one by one; whereas Từ Nhạc Ngô, in his commentary, holds that the cycle takes the direction of the branch as primary (Dần Mão Thìn the eastern direction, Tị Ngọ Mùi the southern direction...) and must be considered across the whole ten years. On Vietnamese-language BaZi forums, these two approaches are still compared against each other, and some people use precisely that difference to test whether a chart should be read as a strong self or a weak self.
This article does not pick a side in advance. The approach here is to present both, and when interpreting a specific chart, to state clearly which approach is being followed, so that the reader is not confused between two contradictory results.
Five Years Stem, Five Years Branch, or the Whole Ten Years?
A common practical question is how the stem and branch divide the ten years of a major cycle between them. According to Ho Peng Yoke (2003), Chinese Mathematical Astrology: Reaching Out to the Stars, RoutledgeCurzon, there is a way of splitting in half: the first five years lean toward the stem, the latter five toward the branch. There is another way that sees the stem and branch as both present throughout the ten years, differing only in degree of influence. There is yet another way that sees the stem as the opening portion and the branch as the closing portion, emphasizing whichever part depending on what is being asked.
No convention is accepted by all schools. What one should do when interpreting is to state clearly which division is being used, and stay consistent throughout the interpretation, rather than taking the stem at one moment and the branch at another according to the desired result.
What Do the Annual Pillar and the Meeting of Year and Cycle Mean?
The annual pillar is the stem and branch of a specific year, running on top of the major cycle currently in effect. The meeting of year and cycle is the case where the stem and branch of the annual pillar coincide with the stem and branch of the major cycle, that is, that year and that cycle carry the same pair of characters. This phrasing describes a phenomenon of exact overlap in terms of stems and branches, and its degree of influence still has to be read through the favorable and unfavorable elements of the original chart; it is not automatically good or bad.
There is an approach holding that when interpreting the annual pillar, the branch of the annual pillar plays the decisive role for the main fortune or misfortune, while the stem of the annual pillar is usually only secondary. The same material also notes an exception: if the stem of the annual pillar is in a prosperous state, is produced by the branch of the annual pillar or shares its element, then it takes a significant part in the generation and control with the chart and the major cycle, slightly altering the situation. Also according to that material, when the stem of the annual pillar is a favorable element but is controlled or combined away by another god in the chart, the good cannot manifest, and conversely if it is an unfavorable element but is controlled, the bad is also reduced. This is a graded way of reading, not a fixed formula of addition and subtraction.
How Does One Interpret an Annual Pillar That Clashes with or Controls the Major Cycle?
When the annual pillar clashes with or controls the major cycle, the general principle is to consider whether both sides are favorable or unfavorable before speaking of the outcome. There is an approach holding that if the branch of the annual pillar is a favorable useful god and is further supported by the major cycle, that year is smooth; if the branch of the annual pillar is an unfavorable element and the major cycle supports it, that year is unfavorable; if the branch of the annual pillar is a favorable element but is controlled by the major cycle, the good is reduced, sometimes only to an ordinary level; and if the branch of the annual pillar is an unfavorable element but is controlled by the major cycle, the bad is also reduced. This material also emphasizes the resonance between the annual pillar and the major cycle, while noting that one must also consider punishment, clash, meeting and combination between the annual pillar and the pillars in the chart.
It should be said clearly that this is the reading of one specific material, not a rule recognized by all schools. In practice, the same year of clash between the annual pillar and the major cycle can be read by one school as a strong upheaval and by another as the removal of a blockage, depending on the favorable or unfavorable nature of the relevant stems and branches in the chart being examined.
Why Can the Major Cycle Not Be Read Apart from the Original Chart?
The major cycle is only additional stems and branches arriving, while the capacity to respond to those stems and branches lies in the original chart. The same Tân Mùi major cycle will be read quite differently for a person whose original chart needs the metal element than for one whose original chart already has too much metal. The same annual pillar clashing with the month pillar will be read differently for a person whose month pillar is a favorable element than for one whose month pillar is an unfavorable element. If the major cycle is separated from the original chart, the interpreter is left with only a neutral sequence of stems and branches, with no basis on which to speak of fortune or misfortune.
The practical consequence is that the order of interpretation must be fixed: establish the original chart, determine strength or weakness and the useful god, establish the major cycle, and only then lay the annual pillar on top. Reversing the order, for example starting from a year in which an event occurred and working backward to the useful god, is a way of working that easily produces arbitrary conclusions.
Where Do the Schools Still Differ?
Beyond the question of whether the stem or the branch carries more weight, there are at least three practical points of difference worth noting.
- Rounding the starting age of the cycle. Some schools keep the exact number of years, months and days after conversion, some round up or down for convenience, and some convert the remainder further into months and then drop the days. The difference is only a few months but can push an event into the previous or the following year.
- Reckoning by nominal age or actual age. Nominal age adds one year from the moment of birth, actual age counts from the birth date. Which age a major cycle table is recorded in depends on the chart-maker's convention, and when comparing two tables from two different sources one must check which age they are using before concluding that the two differ.
- Whether to use the minor cycle at all. According to Ho Peng Yoke (2003), Chinese Mathematical Astrology: Reaching Out to the Stars, RoutledgeCurzon, some schools drop the minor cycle entirely and use only the major cycle plus the annual pillar, while some still use it. This is a difference in the scope of the system, not a difference in the method of calculation within the same system.
Practical Conclusion
To establish and read a BaZi major cycle correctly, four steps must be carried out in order: determine the direction from the gender and the yin-yang of the year stem, calculate the starting point of the cycle from the distance to the solar term at the ratio of three days to one year, build the sequence of stems and branches with the major cycle function rather than by hand, and read each cycle by placing it beside the useful god and the favorable and unfavorable elements of the original chart before laying the annual pillar on top. Any conclusion about fortune or misfortune should be presented only as a tendency toward smoothness or difficulty within a period, with the convention being used stated clearly, because the schools themselves have not yet reached agreement on the core points of this method of reading.
