# Kua Number Calculator: Your Gua Number, Group and Favourable Directions

Find your Kua (Gua) number with the Eight Mansions formula, using exact Start of Spring dates, plus your East or West group and four favourable directions.

Interactive tool: https://lookup.sg/tools/kua-number-calculator

## How this works
The Kua number (命卦, also spelt Gua) comes from the Eight Mansions (八宅) school of feng shui. It uses your birth year counted from Start of Spring (立春), which falls on 3, 4 or 5 February, so anyone born in January or early February uses the previous year. The calculator looks up the exact Start of Spring for every year from 1901 to 2099 (generated with the lunar-javascript library and checked against Hong Kong Observatory calendar tables), converted to Singapore time.

The usual recipe: add the last two digits of the year until you get one digit. Men born in the 1900s take that from 10 (from 9 for 2000 onwards); women add 5 (6 for 2000 onwards) and reduce to one digit again. There is no Kua 5 in this system: men with 5 take 2, and women take 8. The calculator uses an equivalent formula, checked against this recipe for every year from 1900 to 2099.

Kua numbers 1, 3, 4 and 9 form the East group and 2, 6, 7 and 8 the West group. Each number has four favourable directions (Sheng Qi, Tian Yi, Yan Nian and Fu Wei) and four unfavourable ones (Huo Hai, Wu Gui, Liu Sha and Jue Ming), from the eight trigrams of the Later Heaven arrangement. This is cultural tradition, and different feng shui schools use different methods.

## FAQs
### How do I calculate my Kua number?
Add the last two digits of your birth year down to one digit, then (for the 1900s) take it from 10 if you are male or add 5 if you are female. For 1990: 9 + 0 = 9, so a man is Kua 1 and a woman is 5 + 9 = 14, 1 + 4 = 5, which becomes Kua 8.

### What is my Kua number if I was born in January?
Use the previous year, because the Kua year starts at Start of Spring (about 4 February). A man born on 20 January 1990 counts as born in 1989: 8 + 9 = 17, 1 + 7 = 8, and 10 minus 8 gives Kua 2.

### What Kua number is someone born in 2000?
Kua 9 for a man and Kua 6 for a woman, if born after Start of Spring on 4 February 2000. From 2000 the recipe takes the digit sum from 9 for men and adds 6 for women.

### What is the difference between the East and West groups?
Kua 1, 3, 4 and 9 are East group, with favourable directions north, south, east and south-east. Kua 2, 6, 7 and 8 are West group, with favourable directions west, north-west, south-west and north-east.

### Why is there no Kua number 5?
Five sits in the centre of the Lo Shu square, which has no direction. In the Eight Mansions system men with 5 use Kua 2 (south-west) and women use Kua 8 (north-east).

## Sources
- [Hong Kong Observatory: Gregorian-Lunar calendar conversion tables (Start of Spring dates)](https://www.hko.gov.hk/en/gts/time/conversion.htm)
- [lunar-javascript (MIT licence), used to generate the Start of Spring table](https://github.com/6tail/lunar-javascript)

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