A kua number is a single digit from 1 to 9 worked out from your birth year and your sex. It is not a business number in itself. What it does is enter the Lo Shu grid as a third figure alongside the driver and the conductor, and that extra entry can fill a cell that would otherwise be empty — which is why two founders born on the same day can end up with different grids.
That is the short version. The longer version matters because the kua number is the figure most often quoted wrongly online, and because the rule this site's calculators apply is not the only rule in circulation.
How to calculate a kua number
The calculation has two steps. Reduce the birth year to a single digit, then apply one of two formulas depending on sex.
Step one — reduce the year. Add the four digits of the birth year and keep adding until one digit is left.
For 1988: 1 + 9 + 8 + 8 = 26, and 2 + 6 = 8. The year root is 8.
Step two — apply the formula.
- For a man, subtract the year root from 11 and reduce the answer to one digit.
- For a woman, add 4 to the year root and reduce the answer to one digit.
A man born in 1988 takes 11 − 8, which is 3. His kua number is 3.
A woman born in 1988 takes 8 + 4 = 12, and 1 + 2 = 3. Her kua number is also 3 — 1988 is one of the years where the two formulas meet.
Take 1992 instead. The year root is 1 + 9 + 9 + 2 = 21, and 2 + 1 = 3. A man born in 1992 takes 11 − 3 and lands on 8. A woman born in 1992 takes 3 + 4 and lands on 7.
The kua number for every year root
Because the formula depends only on the reduced year, there are just nine possible pairs. This table is the whole rule, and it is generated from the same code that runs the Lo Shu grid calculator.
| Year root | Example birth years | Male | Female |
|---|---|---|---|
| 1 | 1990, 1981, 1972 | 1 | 5 |
| 2 | 1991, 1982, 1973 | 9 | 6 |
| 3 | 1992, 1983, 1974 | 8 | 7 |
| 4 | 1993, 1984, 1975 | 7 | 8 |
| 5 | 1994, 1985, 1976 | 6 | 9 |
| 6 | 1995, 1986, 1977 | 5 | 1 |
| 7 | 1996, 1987, 1978 | 4 | 2 |
| 8 | 1997, 1988, 1979 | 3 | 3 |
| 9 | 1998, 1989, 1980 | 2 | 4 |
Two things in that table surprise people. The first is that a kua number of 5 is returned as 5; the variant that reassigns it to 2 for men and 8 for women is not applied by the calculators here. A reader who runs the tool and gets 5 is therefore seeing the method this site actually uses rather than a rounding of it.
The second is that the birth year is taken exactly as written on the birth certificate. Some schools move anyone born in January or early February back into the previous lunar year before reducing it; that is a convention the calculators here do not use, and an article that quietly applied it would contradict the tool sitting one click away.
What the kua number actually does in a business chart
This is where most write-ups stop being useful, because they treat the kua number as a fortune in its own right. In the chart this site builds, it does one concrete job: it is written into the Lo Shu grid.
The grid is a fixed three-by-three arrangement of the digits 1 to 9. Every digit of the birth date is written into its matching cell, and then three derived figures are added — the driver (the day of the month reduced), the conductor (the whole date reduced) and the kua number. A cell with nothing in it is a missing number, and missing numbers are what the grid is mostly read for.
So the kua number is a third chance to fill a cell. Sometimes it changes nothing because the digit was already present. Sometimes it is the only entry in that cell, and removing it would change the reading.
A worked example
Take a founder born on 12 April 1988, male.
- Driver: the day is 12, so 1 + 2 = 3.
- Conductor: 1 + 2 + 0 + 4 + 1 + 9 + 8 + 8 = 33, and 3 + 3 = 6. Written properly that is 33/6.
- Kua: the year root is 8, and for a man 11 − 8 gives 3.
The digits written into the grid are the date digits 1, 2, 4, 1, 9, 8 and 8 — zeros are not placed, because there is no zero cell — plus the driver 3, the conductor 6 and the kua 3.
| 4 | 9 | 2 |
| 33 | — | — |
| 88 | 11 | 6 |
Reading the empty cells: 5 and 7 are missing. The 3 appears twice only because the driver and the kua number happen to agree, which is a repetition worth noticing rather than a doubling of strength.
Now take a founder born on 9 November 1992, female.
- Driver: the day is 9, so the driver is 9.
- Conductor: 0 + 9 + 1 + 1 + 1 + 9 + 9 + 2 = 32, and 3 + 2 = 5, written 32/5.
- Kua: the year root is 3, and for a woman 3 + 4 gives 7.
| — | 9999 | 2 |
| — | 5 | 7 |
| — | 111 | — |
Here the kua number is doing real work. The 7 cell is filled by the kua number alone. Without it the grid would show five empty cells instead of four, and the reading of this founder's chart would shift. You can reproduce both of these grids in the Lo Shu grid tool by entering the date and the sex.
Why the kua number needs a sex and the other numbers do not
The driver and the conductor come from the date alone. The kua number is the only figure in this system that asks for sex, and that has two practical consequences.
The first is that a company has no kua number. A business has a registration date but no sex, so when the grid is built for an incorporation date rather than a person, only the date digits, the driver and the conductor go in. Any published grid for a company that shows a kua entry has borrowed a figure from somewhere it does not exist.
The second is that co-founders born in the same year will usually have different kua numbers, and this is the one place where the two charts diverge for a reason that has nothing to do with the date. The table above shows the pairs meeting only at year root 8.
How the kua number relates to the driver and the conductor
They are independent figures answering different questions, and the driver and conductor guide covers the first two in full. In short:
| Figure | Derived from | Asks |
|---|---|---|
| Driver | Day of the month, reduced | How the founder behaves day to day |
| Conductor | The whole date, reduced | The longer arc of the working life |
| Kua | Birth year and sex | Which cell of the grid gets a third entry |
A founder whose driver, conductor and kua number are all the same digit has a chart with heavy repetition in one cell and correspondingly more empty cells elsewhere. That is not a verdict; it is a shape. The core calculators report the three figures themselves; the Lo Shu grid tool is what draws the shape they make.
The directional reading, and why no calculator here produces it
Most of what is written about the kua number online is not about the grid at all. It is about direction: the idea that each kua number is assigned a set of supportive and unsupportive compass bearings, and that a desk should face one of them.
That material belongs to a different tradition from the one this site computes. It is worth stating plainly rather than pretending it does not exist, so here is the shape of it, with the honest caveat attached to every line.
| Kua | Grouping used by that school | Bearings that school calls supportive |
|---|---|---|
| 1 | East group | South-east, east, south, north — the calculators here do not produce these |
| 3 | East group | South, north, south-east, east — the calculators here do not produce these |
| 4 | East group | North, south, east, south-east — the calculators here do not produce these |
| 9 | East group | East, south-east, north, south — the calculators here do not produce these |
| 2 | West group | North-east, west, north-west, south-west — the calculators here do not produce these |
| 6 | West group | West, north-east, south-west, north-west — the calculators here do not produce these |
| 7 | West group | North-west, south-west, north-east, west — the calculators here do not produce these |
| 8 | West group | South-west, north-west, west, north-east — the calculators here do not produce these |
The reason for the caveat is a house rule rather than a judgement about the tradition. This site's whole claim is that its articles agree with its calculators, and there is no calculator here that returns a bearing. Publishing a direction table without saying so would make the prose the only authority for it, which is exactly the situation the rule exists to prevent. If you want to work with directions, work with a source that specialises in them — and be aware that the kua number it starts from may differ from the one here if it applies the lunar-year adjustment or the reassignment of 5.
Note also that a kua number of 5 has no row above. In the directional school it is the number that gets reassigned, and since the reassignment is not something the calculators here do, there is no honest row to write.
Using the kua number when you are actually choosing something
A founder rarely needs the kua number on its own. It matters when it changes the count of missing numbers, because that count is what feeds the rest of the reading. Three practical cases:
Choosing a business name. The name total is graded against the driver and the conductor, not the kua number. Run the name through the business name analyser and the kua number will not appear in the verdict, because it does not belong there. If an analysis tells you a name suits your kua number, it is using a rule this method does not have.
Reading the grid for gaps. Here it counts, and it is the only place it counts. The founder born on 9 November 1992 above has four empty cells with the kua number included and five without it, and missing numbers in the Lo Shu grid are read as areas needing deliberate effort rather than as faults.
Comparing co-founders. Two people born in the same year, one male and one female, will usually get different kua numbers and therefore different grids from very similar dates. That difference is real within the method, but it is a difference in grid shape, not a compatibility verdict — compatibility between two people is worked out from their driver and conductor numbers by the partnership compatibility tool — the founder compatibility tool answers a different question, grading one founder against a trading name.
Where the kua number runs out
Several things are worth saying plainly.
The kua number is the least agreed-upon figure in this whole system. The formula splits on sex, the treatment of 5 splits by lineage, and the year boundary splits by calendar. Where the driver and the conductor are arithmetic anyone can check, the kua number is arithmetic plus a set of conventions, and reasonable practitioners land on different digits for the same person. This site picks one convention and applies it consistently; that is the most that can honestly be claimed for it.
It is also the figure with the least to say. In the chart built here it contributes one entry to one cell. It does not carry a business meaning of its own, it does not grade a name, and it does not rank a launch date. Any reading that leans heavily on it is leaning on a thin figure.
And none of it forecasts a commercial result. A grid describes tendencies the tradition associates with a chart. It does not know your market, your pricing or your cash position, and nothing here should be treated as financial advice. Use it the way you would use a personality inventory: as a prompt for reflection, alongside the evidence that actually decides whether a business works. The methodology page sets out which parts of this system are sourced and which are not.
Frequently asked questions
What is my kua number?
Add the four digits of your birth year and reduce them to one digit. Subtract that from 11 and reduce again if you are male; add 4 to it and reduce again if you are female. For a birth year of 1990 the year root is 1, so a man has a kua number of 1 and a woman has a kua number of 5. The Lo Shu grid tool does both steps for you.
Does a company have a kua number?
No. The formula needs a sex, and a company does not have one. When a grid is built from an incorporation date, only the date digits, the driver and the conductor are placed. A company grid showing a kua entry has taken the figure from a founder's chart and attached it to the business, which mixes two different charts.
Is a kua number of 5 a problem?
No, and it is not converted here either. The calculators return 5 as 5. Several lineages reassign it to 2 for men and 8 for women, which is a variant this site does not apply. If another source gives you a different digit than the tool here does, this is usually why.
Do the kua number and the driver number mean the same thing?
No. The driver comes from the day of the month and describes day-to-day working temperament. The kua number comes from the birth year and sex and exists in this method only to add a third entry to the Lo Shu grid. They answer different questions and are often different digits.
Why do men and women get different kua numbers?
Because the tradition uses two formulas, one subtracting the year root from 11 and one adding 4 to it. They agree only at year root 8. It is the only figure in this system that asks for sex at all, which is part of why it is the most contested one.