TL;DR: Bát Trạch assesses desk direction by age by calculating the cung mệnh (quái số) from birth year and gender, then comparing it with the eight directions East, West, South, North, Northeast, Northwest, Southeast, Southwest to choose directions in the Sinh khí, Thiên y, Diên niên, Phục vị groups. This is a convention of one feng shui school, not a scientific conclusion. The article presents the calculation, a table of the eight directions by cung mệnh, how to measure desk direction with a compass, and points where books still differ.
What is the basis for Bát Trạch assessing desk direction by age?
Bát Trạch is a feng shui school that uses the eight trigrams of the I Ching as a framework of directions, then divides people and houses into two groups, Đông tứ mệnh and Tây tứ mệnh, to discuss good and bad fortune. For a desk, this school considers the direction the person faces (the direction the face looks or the direction of the back, depending on the branch) according to the owner's cung mệnh. That cung mệnh is calculated from birth year and gender, hence the shorthand of looking at desk direction by age.
It must be said right away so readers do not misunderstand: this is a convention of a metaphysical school, not a verified causal relationship. For the same age, books may give different directions, and choosing a desk direction also depends on the actual layout, lighting, walkways, and door position. This article follows the common Bát Trạch convention circulating in Vietnam, cross-checks with the cited books, and notes where sources disagree.
How is cung mệnh calculated from birth year?
Cung mệnh (also called quái mệnh, quái số) takes the lunar birth year and gender as inputs. The common method: add the last two digits of the birth year and keep adding until one digit is left. For people born from 1900 to 1999, a male subtracts that number from 10 and a female adds 5 to it; for people born from 2000 onward, a male subtracts it from 9 and a female adds 6. If the result still has two digits, add them again until one is left; a male result of 0 counts as 9. The quái số runs from 1 to 9, where 5 is mapped to 2 (Khôn) for males and 8 (Cấn) for females. Some books use a different formula but give the same result, because the essence is taking the remainder of the birth year modulo 9.
There are two easy mistakes. First, the birth year must be considered by the lunar calendar: someone born in January or early February of the solar calendar, before Tết Nguyên Đán, belongs to the previous lunar year, so the calendar must be checked. Second, gender in Bát Trạch is only male and female; other cases have no separate convention in old books, and current practitioners often ask the client which biological sex to use.
Example of this calculation: a male born in 1990, add 9+0 = 9, take 10 minus 9 to get 1, quái số 1 is Khảm, belonging to Đông tứ mệnh. A female of the same year: 5 plus 9 gives 14, then 1+4 = 5, and for females 5 becomes 8, so quái số 8 is Cấn, belonging to Tây tứ mệnh. A single birth year already puts the two genders in different groups, so one cannot speak of a good desk direction by age while ignoring gender.
How are the eight good and bad directions of each cung mệnh ranked?
Each quái số has four good directions and four bad directions, ranked as Sinh khí, Thiên y, Diên niên, Phục vị (good) and Tuyệt mệnh, Ngũ quỷ, Lục sát, Họa hại (bad). This order is derived from five-element relationships and line changes among the eight trigrams; it is a convention of the Bát Trạch school, not an independently verifiable calculation like calendrical astronomy.
The table below is a lookup of the eight directions by quái số, compiled from the common presentation in Bát Trạch books circulating in Vietnam. The direction column is given by compass, each direction corresponding to a trigram in the later heaven arrangement.
| Quái số | Cung mệnh | Group | Four good directions (Sinh khí, Thiên y, Diên niên, Phục vị) | Four bad directions (Tuyệt mệnh, Ngũ quỷ, Lục sát, Họa hại) |
|---|---|---|---|---|
| 1 | Khảm | Đông tứ mệnh | Southeast, East, South, North | Southwest, Northeast, Northwest, West |
| 2 | Khôn | Tây tứ mệnh | Northeast, West, Northwest, Southwest | North, Southeast, South, East |
| 3 | Chấn | Đông tứ mệnh | South, North, Southeast, East | West, Northwest, Northeast, Southwest |
| 4 | Tốn | Đông tứ mệnh | North, South, East, Southeast | Northeast, Southwest, West, Northwest |
| 6 | Càn | Tây tứ mệnh | West, Northeast, Southwest, Northwest | South, East, North, Southeast |
| 7 | Đoài | Tây tứ mệnh | Northwest, Southwest, Northeast, West | East, South, Southeast, North |
| 8 | Cấn | Tây tứ mệnh | Southwest, Northwest, West, Northeast | Southeast, North, East, South |
| 9 | Ly | Đông tứ mệnh | East, Southeast, North, South | Northwest, West, Southwest, Northeast |
This table is only a lookup tool. What matters is knowing which book you are looking up, because the order of the four good directions may be reversed between books, and some books emphasize the Sinh khí direction more than the other three.
Which direction should be understood as the desk direction?
This is where books disagree, and it must be stated clearly. Three interpretations are current. The first takes the direction the seated person faces, that is, the direction of the body. The second takes the direction of the back, that is, the opposite direction. The third takes the direction of the desk surface or the direction of the office door.
The book Sử dụng la bàn, when discussing measuring building direction, takes the back direction of the structure as the basis for discussion, and uses the cross lines or Thiên tâm thập đạo on the compass to determine it[1].
For a desk, the common understanding in Bát Trạch books is to take the direction the seated person faces, because that is the "qi intake" direction of the worker. The sitting-facing method also takes the back direction into account. Readers should choose one convention and keep it consistent, rather than sometimes considering the facing direction and sometimes the back direction to get both good.
How to measure desk direction correctly?
Measuring direction is the most error-prone step, because modern compasses are affected by steel, screens, speakers, and phones placed nearby. Sử dụng la bàn advises placing the compass level, possibly spreading a thick layer of rice under the base for balance, and placing the outer plate against the building wall to measure, though this method is slightly off[1]. For a desk in an enclosed room, measure in the middle of the room or at the desk position, avoid placing the compass close to metal, and measure twice at two different positions to cross-check.
Sử dụng la bàn also gives a method for determining directions according to Bát Trạch: place the compass at the center point of the building floor plan, divide the plan into eight directions according to the eight trigrams, then see which sector the main door or object position falls in to discuss good and bad fortune[1]. For a desk, one can do similarly: determine the room center, divide into eight sectors, then see which sector the desk is in and which sector the seated person faces.
A note on units: each direction in the eight trigrams is not a line but a range. Phong thủy thực hành trong xây dựng và kiến trúc nhà ở states that each good or bad direction spans 45 degrees and is divided into three sectors of 15 degrees each, forming the 24 direction sectors of the compass, and says that if circumstances do not allow detailed measurement, choosing one of the eight main directions is good enough[2].
How should specific cases be handled?
The desk cannot be rotated to a good direction
This is the most common case in rented offices with fixed layouts. Phong thủy thực hành trong xây dựng và kiến trúc nhà ở acknowledges that in many places one must follow planning regulations and no longer has the right to choose the qi direction as desired, so one can only rely on feng shui methods to address shortcomings in house direction, door direction, kitchen direction, and altar direction[2]. For a desk, the Bát Trạch approach is usually to keep the desk direction but adjust the sitting direction, or add a screen, or switch to considering the direction of the whole room instead of the desk.
A Đông tứ mệnh person sits in a Tây tứ direction
By Bát Trạch logic, this is a bad direction and should be avoided if rotation is possible. But remember this is a school's convention, not a warning about health or finances. If rotation is not possible, prioritize the direction facing the door or the direction with natural light, because actual working conditions matter more than chasing a direction in the lookup table.
Two people in the same room with different cung mệnh
Bát Trạch has no general rule for multiple people sharing one desk. Followers of the school usually take the person who directly uses the desk as the owner, or the person with main responsibility in the room. For spouses or colleagues sitting opposite each other, each person considers their own sitting direction, not assigning the desk direction to both.
Where do the schools differ?
The first difference is the understanding of direction, already mentioned above: facing direction or back direction. The second difference is whether to also consider the flying stars. Bát Trạch only considers the eight directions by cung mệnh, while the Huyền Không Phi Tinh school also considers the period, mountain, and direction of the whole house. Hồ Kinh Quốc and colleagues' book Tìm hiểu Cổ dịch Huyền không học (2001) states that by school, compasses divide into the tam nguyên plate and the tam hợp plate; on choosing days, it says one only needs to be clear that the purpose is to avoid inauspicious qi, especially that of the year and month, because if every day and every hour had to follow the rules, people would have no way to get anything done[3]. That spirit applies to choosing desk direction too: do not let rules override the actual work.
The third difference is the priority order of the four good directions. Some books put Sinh khí first and consider it the only direction worth following, while others hold that for a desk one should prioritize Thiên y or Phục vị because they relate to health and stability. There is no consensus, and the books themselves give no verifiable reason.
Should desk direction by age be emphasized?
No. Bát Trạch is a convention system with internal logic, worth consulting as a way of arranging space, but there is no basis to assert that desk direction determines productivity or success. Factors with clearer influence on work are lighting, noise, posture, distance to the door, and privacy. If the Bát Trạch desk direction coincides with one of these factors, good; if it conflicts, prioritize actual working conditions.
Gợi ý của Nhật Nguyệt: use the lookup table as a final reference step, after choosing a desk position that is reasonable for lighting and walkways. If the cung mệnh gives a good direction but that direction makes the seated person turn their back to the door or block the walkway, keep the old position and adjust by sitting direction or by rearranging the room.
