The method of arranging the major cycle: For a male born in a yang year, the cycle is arranged in the forward direction, while for a female born in a yin year, it is arranged in the reverse direction. Usually, eight major cycles are arranged because each major cycle governs ten years, and eight cycles mean eighty years, which is considered long life. Below is an example of arranging eight major cycles:
A male born in the year of Geng Xu and the month of Ji Mao: as he was born in a yang year, his major cycles are: Geng Chen, Xin Si, Ren Wu, Gui Wei, Jia Shen, Yi You, Bing Xu, Ding Hai.
A female born in the year of Geng Xu and the month of Ji Mao: as she was born in a yang year, her major cycles are: Wu Yin, Ding Chou, Bing Zi, Yi Hai, Jia Xu, Gui You, Ren Shen, Xing Wei.
A male born in the year of Ding You and the month of Jia Chen: as he was born in a yin year, his major cycles are: Gui Mao, Ren Yin, Xin Chou, Geng Zi, Ji Hai, Wu Xu, Ding You, Bing Shen.
A female born in the year of Ding You and the month of Jia Chen: as she was born in a yin year, her major cycles are: Yi Si, Bing Wu, Ding Wei, Wu Shen, Ji You, Geng Xu, Xin Hai, Ren Zi.
Cycle Calculation: The method of calculating the starting age of the major cycle is three days equal to one year, meaning one day equals four months, and one hour equals five days.
In traditional calculation, the timing of entering and leaving the major cycle is based on the assumption that each solar term lasts fifteen days, totaling 360 days per year, which differs from the actual solar year of 365 days, 5 hours, 48 minutes, and 45 seconds. Therefore, there must be some errors. Modern astrologers calculate the exact time of entering and leaving the cycle based on the number of days and hours after a particular solar term, but this is still not accurate.
The accurate calculation method is: 365.242194 / 360 = 1.01456165, so the number of days calculated by the ancient method from the birth time to the solar term must be multiplied by 1.01456165 for more accuracy.

In Ba Zi astrology, one major cycle governs ten years, hence called the ten-year major cycle.
Fate, major cycle, feng shui, accumulated merits, and education—this list mentions "major cycle," which refers to the major cycle we usually talk about. The major cycle has a significant impact on our lives, second only to our destiny itself.
Entering a new major cycle means the transition from one ten-year period to another or from a five-year minor cycle to a new one. This transition is known as the "entering of the cycle." Why is this time important? Because each cycle has different heavenly stems and earthly branches, meaning the Five Elements environment changes for a person during each cycle. Transitioning from the old to the new environment requires an adaptation period. If this adaptation is not smooth, some unusual events may occur. This is similar to changing jobs: after working in a place for a long time, one becomes familiar with the work and colleagues. Suddenly moving to a new workplace, where both work and people are unfamiliar, one must be careful. If the adaptation is not good, one might feel overwhelmed, just like saying "start well" or "begin properly." So, this day is like the first day of the first lunar month, and one must be happy, otherwise the whole year could be unlucky. Similarly, if the day of entering the major cycle is unfavorable, the next ten years might also be problematic.
To calculate the start time of the major cycle, one starts from the birth date and time. For a male born in a yang year or a female born in a yin year, the cycle is calculated in the forward direction; for a male born in a yin year or a female born in a yang year, it is calculated in the reverse direction. (Note: Yang years and yin years are determined by the stem: Jia, Bing, Wu, Geng, and Ren are yang years; Yi, Ding, Ji, Xin, and Gui are yin years). Forward calculation means counting from the birth date and time to the next solar term's time. Count how many days and hours have passed, then convert three days into one year, one day into four months, and one hour into five days. This way, the accurate time of entering the major cycle can be calculated. Reverse calculation is different in that it counts backward from the birth date and time to the previous solar term's time, using the same method as forward calculation. For example, a male born on the fifth day of the eleventh month in the year of Jia Wu at the wei hour. As this is a yang year male, the cycle is calculated in the forward direction. From the birth date and time, count to the next solar term, which is the Great Snow term in the year of Jia Wu, occurring on the fourteenth day of the eleventh month at the zi hour. Counting from the fifth day of the eleventh month at the wei hour to the fourteenth day of the eleventh month at the zi hour, the total is eight days and five hours. Convert three days into one year, resulting in two years and two hundred and ninety days, which is counted as three full years. Thus, it should be expressed as: every year when the heavenly stem is Ding or Ren, the cycle is entered on August 25th at the wei hour. "Entering and leaving" refers to transitioning from the old cycle to the new one. For example, a female born on the twenty-sixth day of the third month in the year of Bing Wu at the chen hour. As this is a yang year female, the cycle is calculated in the reverse direction. Starting from the birth date and time, count backward to the previous solar term. According to calculations, the cycle is entered every year when the heavenly stem is Jia or Ji, on August 26th at the chen hour.

In Ba Zi cycle calculation, the good or bad years of the ten-year major cycle are determined. Earlier books stated that each cycle consists of the heavenly stem and earthly branch, with the heavenly stem governing the first five years and the earthly branch governing the last five years. Another theory suggests that since the earthly branch is particularly emphasized in the major cycle, some say the heavenly stem governs four years and the earthly branch six years, while others say the heavenly stem governs three years and the earthly branch seven years. These are all incorrect. In Ba Zi calculation, since the major cycle begins from the month's term and moves forward, it proceeds to the next month's term. When moving backward, it proceeds to the previous month's term. Since the heavenly stem and earthly branch of the month's term govern the entire month, there is no rule that the heavenly stem governs the first half of the month and the earthly branch governs the second half. However, when used for the major cycle, the heavenly stem and earthly branch are separated to govern different periods. Therefore, it is correct that the heavenly stem and earthly branch together govern ten years.
If the heavenly stem and earthly branch are balanced and mutually supportive, their power is equal. If the heavenly stem overpowers the earthly branch, the heavenly stem's power is stronger. If the earthly branch overpowers the heavenly stem, the earthly branch's power is stronger. From the perspective of the individual, if both the heavenly stem and earthly branch are favorable elements, the ten years of the major cycle will be entirely auspicious. If both are unfavorable elements, the ten years will be entirely adverse. If one is favorable and the other is unfavorable, the ten years will be half good and half bad. This is the most accurate understanding.
However, determining the auspiciousness or inauspiciousness of the major cycle is easier for the heavenly stem than for the earthly branch. The heavenly stems are straightforward: Jia is only Jia, Yi is only Yi. However, the earthly branches contain various hidden elements, which must be carefully studied and analyzed. For example, in the寅 (Yin) cycle, if the original chart contains Jia, Bing, or Wu, one should first examine which heavenly stem is revealed by the earthly branch. If the heavenly stem is Jia, the cycle is purely wood; if it is Bing, the cycle is mostly fire; if it is Wu, the cycle is half earth. The same logic applies to other earthly branches. Additionally, the relationship between the heavenly stem and the original chart's stems and branches is clear, only considering the mutual generation and overcoming. However, the relationship between the earthly branch and the original chart's stems and branches involves not only generation and overcoming but also mutual conflicts, combinations, punishments, and harms, which are difficult to distinguish immediately.