TL;DR: Checking today's good and bad days by the lunar calendar means looking up the day's can chi, trực, auspicious and inauspicious stars, and hoàng đạo hours to choose when to do something important. This is a custom rooted in calendrical practice, still widespread through the vạn sự almanac, but many researchers treat it as cultural belief rather than a verified law. A good day does not guarantee results, and a bad day does not decide in place of each person's preparation.
What is checking today's good and bad days by the lunar calendar?
Checking today's good and bad days by the lunar calendar means looking up the current day's calendrical information, including the day's can chi, trực, auspicious and inauspicious stars, and the hoàng đạo time frames, to weigh when to do something important. In the can chi system, each day is named by a pair of a heavenly stem and an earthly branch, running in a 60-day cycle.
Vietnamese people have long checked good and bad days through the vạn sự almanac. In a study of the Vietnamese custom of offering to the stars to ward off misfortune in the northern delta, Lê Đức Hạnh reports that both ordinary people and ritual masters used the vạn sự almanac as their official reference: they relied on it to identify inauspicious or auspicious stars, predict good and bad outcomes, and choose good and bad days within one year or several years. Each almanac runs over 100 pages, 13 by 19 cm, and is usually sold one or two months before the solar new year.
It is necessary to distinguish two different layers within the same calendar page. The first layer is calendrical data: the lunar day, can chi, solar terms, and hours. The second layer is the interpretation of good and bad: whether to marry or avoid on this day, which star to offer to. The first layer can be calculated and cross-checked against a printed calendar or an independent table; the second layer belongs to the conventions of each book and each school, and the books do not fully agree with one another.
Why is a day considered good or bad?
A day is considered good or bad based on the combination of several layers of calendrical information, not just one single factor. In Việt Nam phong tục (1915), Phan Kế Bính recorded how Vietnamese people in the early 20th century chose dates: every task required choosing a day matching one's fate, avoiding bad days, and he listed groups of good days such as lục hợp days, Thiên đức, Nguyệt đức, Thiên ân, Thiện hỉ, Lộc mã, Hoàng đạo days, along with groups of bad days such as thớp ác đại bại days, tứ lụ days, tứ tuyệt days, and trực phá and trực nguy days.
The main layers usually checked include:
- The day's can chi: the day's pair of heavenly stem and earthly branch, used to examine the relationship with the birth year and birth month can chi of the person doing the task.
- Trực: twelve trực rotating by day, each with tasks to do and to avoid.
- Auspicious and inauspicious stars in the day: auspicious and inauspicious stars placed by each book's own rules.
- Hoàng đạo and hắc đạo hours: six good hours and six bad hours in the day, calculated by the day's earthly branch.
- Solar terms: time markers based on the Earth's position on its orbit around the Sun, used to determine the month in divination arts.
A notable point is that for the same day, different books may give different conclusions. This does not mean one book is right and one wrong, but reflects that each system places stars and sets rules in its own way.
How to check today's good and bad days by the lunar calendar
Checking today's good and bad days by the lunar calendar involves four steps: determine the lunar day and the day's can chi, look up the trực, look up auspicious and inauspicious stars, then choose the hoàng đạo hour if the task must begin at the right moment. The first step anyone can do: open a lunar calendar or vạn sự almanac and read the line giving the lunar day and the day's can chi.
Step 1: Determine the lunar day and the day's can chi
The lunar day is calculated by the Moon's cycle, while the day's can chi runs in a 60-day cycle. These two cycles are independent, so a lunar day can fall on any of the 60 can chi pairs. The book Bát Môn Thần Khóa notes that many divination methods need to combine the lunar hour at the moment one wants to consult to set the hexagram, and taking the wrong hour means the hexagram is read wrongly, so choosing the date and hour also requires above all the lunar hour.
In the same book, the author records how to convert lunar hours to clock hours according to Vietnam's time zone in the 1960 to 1975 period: each month the start of the Tý hour shifts by about ten minutes, for example in month 11 the start of the Tý hour falls at 0:10, while in months 3 and 7 the start of the Tý hour falls at 0:50. This detail shows that the lunar hour does not stay fixed by the clock but slides with the seasons.
Step 2: Look up the day's trực
The twelve trực are Kiến, Trừ, Mãn, Bình, Định, Chấp, Phá, Nguy, Thành, Thu, Khai, Bế, rotating by day. Phan Kế Bính states clearly that marriage should seek Thiên đức and Nguyệt đức days and avoid trực phá and trực nguy days; travel should seek Lộc mã and Hoàng đạo days and avoid trực phá and trực bế days. Thus the trực is one of the layers used to filter tasks to do and to avoid.
Step 3: Look up auspicious and inauspicious stars in the day
Each day has a number of auspicious and inauspicious stars placed by its own rules. According to Lê Đức Hạnh, the vạn sự almanac fully records astrology, good and bad days, how to choose the first visitor of the new year, bát quái cẩm trạch, judging auspicious and inauspicious stars, human physiognomy, and even methods of reading good and bad from ringing ears and twitching eyes. Based on the vạn sự almanac, people know which star their age is linked to that year, whether that star is good or bad, and how to send off bad stars and welcome good ones.
Step 4: Choose the hoàng đạo hour
The hoàng đạo hours are six good time frames in the day, calculated by the day's earthly branch. Phan Kế Bính recorded four verse lines for calculating hoàng đạo hours by the day's branch: Dần and Thân start from Tý; Mão and Dậu start from Dần; Thìn and Tuất are found at Thìn; Tị and Hợi at Thân; Tý and Ngọ are found at Ngọ; Sửu and Mùi are set at Tuất. He also noted that tasks at their very beginning, such as first setting out, first going out the gate to marry, first building a house, first lowering a coffin, usually all choose the hoàng đạo hour.
The table below summarizes the layers of information usually checked when looking at good and bad days:
| Layer of information | Calculated by | Can it be cross-checked? | Type |
|---|---|---|---|
| Lunar day | Moon cycle | Yes, against a printed calendar | Calendrical data |
| Day's can chi | 60-day cycle | Yes, against a calculation table | Calendrical data |
| Solar terms | Earth's position around the Sun | Yes, against an astronomical calendar | Calendrical data |
| Trực | Rules placed by day | By each book | School convention |
| Auspicious and inauspicious stars | Star-placement rules | By each book | School convention |
| Hoàng đạo hours | Day's earthly branch | By each book | School convention |
How do hoàng đạo and hắc đạo hours differ?
Hoàng đạo hours are six time frames considered favorable, while hắc đạo hours are the remaining six, considered unfavorable. According to the presentation based on Tử Vi Khảo Luận, each day is divided into twelve hours Tý, Sửu, Dần, Mão, Thìn, Tỵ, Ngọ, Mùi, Thân, Dậu, Tuất, Hợi, corresponding to 24 clock hours, of which six are hoàng đạo and six are hắc đạo.
The six hoàng đạo hours carry the names of six stars: Thanh Long, Minh Đường, Kim Quí, Bảo Quang, Ngọc Đường, Tư Mệnh. In this interpretation, each star is linked to a group of tasks: Thanh Long is considered good for many tasks from opening a business and breaking ground to seeking fame; Minh Đường is linked to meeting benefactors and promotion; Kim Quí is especially good for marriage and weddings.
It must be said clearly that this is the understanding of one school, not a rule common to all books. The method of calculating hoàng đạo hours that Phan Kế Bính recorded relies only on the day's branch through four verse lines, without attaching the names of the six stars or specific task groups as in the presentation above. Both approaches yield six time frames, but the interpretation of what to do differs.
Does a good day guarantee that things will go smoothly?
A good day does not guarantee that things will go smoothly, and this is something the old divination books themselves admit. According to Tử Vi Khảo Luận, the folk notion that a day is bad does not necessarily cause significant influence for a person who has a good chart and knows how to arrange things thoroughly; conversely, even a day judged good does not guarantee that everything will go smoothly if that person carries hidden unfavorable factors or behaves unwisely.
In Tử vi đẩu số Mệnh vận phân tích, Từ Tăng Sinh puts the question more bluntly: suppose a person with a bad Phu Thê palace could protect marital happiness simply by choosing an auspicious day to marry, then it would follow that anyone starting a career need only choose a good day to succeed. He concludes that whether a marriage is good depends on the two-way interaction of influence between the two parties; and in the case where the Phu Thê palace is already bad and is compounded by a period of adversity with piled-up sát kỵ, then even marrying on a most auspicious day, the relationship will still run into trouble.
The book Khổng Minh Thần Toán has a similar spirit when discussing bad hexagrams: a bad hexagram is not a death sentence, it is a mirror reflecting a difficult situation, and a wise person looking into the mirror will see what they need to correct[1]. However, it should be noted that this is the discussion of a separate hexagram system, not a common rule for choosing dates.
Where do the schools disagree?
The schools disagree on many points, from how to place stars to how to calculate hours, and the person checking should know which convention they are following. The book Khoa Tử Vi VN Ngày Nay remarks that between books the degree of difference is truly very large, and cites a specific case: with the Hỏa tinh and Linh tinh stars, the Hà Lạc school places them by year and further bases them on month and hour, while the Triệu, Trần, and Thanh schools base them solely on the year.
This difference is not merely academic. It explains why for the same day, two different vạn sự almanacs may record different auspicious and inauspicious stars, and why two date readers may give two opposite conclusions. Calendar users should treat this as reference information from a specific system, not as a universal truth.
Did people in the past distinguish days by solar terms or by lunar months?
People in the past distinguished days by both systems, and traditional divination arts often use solar terms to determine the month. The Bát Tự document presents solar terms as a consequence of the Earth's cycle around the Sun, carrying the weather, climate, and particular energy of each stage of the year; for example, the Lập Xuân solar term signals that spring has arrived, without needing to know whether that day is the 1st or the 15th of the lunar month.
Therefore, when determining the birth month in Bát Tự, one must rely on the solar term in which the person was born, not the lunar date. In the case of a person born on the 21st day of the fourth lunar month but before the Mang Chủng solar term of the fifth month, they are still classified in the fourth month; conversely, a person born on the 1st day of the twelfth lunar month but after the Đông Chí solar term is counted as the first lunar month belonging to the following solar year. This is a very easy point to confuse when checking dates, because the ordinary lunar calendar and the solar-term month do not coincide.
Points to note when using the vạn sự almanac
When using the vạn sự almanac to check dates, note that this almanac contains many kinds of content, and not all are of the same level. Lê Đức Hạnh reports that the vạn sự almanac contains not only sections on good and bad days and auspicious and inauspicious stars, but also bát quái cẩm trạch, human physiognomy, methods of reading good and bad from ringing ears or twitching eyes, a verse for reading chicken feet, and even a table guiding calendar calculation to have a boy or girl as desired.
The fact that one almanac gathers so many kinds of content shows that it is a composite document, not a verified work. Users should separate the calendrical data, which can be cross-checked, from the interpretation of good and bad and other methods of prediction.
Nhật Nguyệt's suggestion when checking today's good and bad days
Nhật Nguyệt's suggestion: if you check good and bad days as a cultural habit, use it as an extra reference layer, do not let it replace your practical plan. For important matters such as signing, surgery, or long-distance travel, the deciding factors remain preparation, information, and the people accompanying you, not the day's can chi pair.
If you want to check correctly, separate two tasks: check calendrical data with a source that can be cross-checked, and check the good and bad part with the awareness that it is the convention of a specific book. When two calendars give different conclusions, that is normal, not a sign that one book is wrong.
Finally, if a day is considered bad and you still must do something important, remember that the old divination books themselves say the outcome depends much more on the person and their preparation than on the day. That is the most clear-headed way to use the vạn sự almanac.
