Saju, bazi and Western astrology

Same root

Both come from the Chinese four-pillar method. The day-stem-centered approach is traditionally credited to Xu Ziping (徐子平) around the 10th century, which is why bazi is also called Ziping (子平). Korea learned it through the classical texts and calls the field myeongri (명리, 命理).

The 10 stems, 12 branches, five elements and ten gods are the same. For the same birth moment and the same rules, a saju chart and a bazi chart show the same eight characters.

Where practice differs

Local time. Korea Standard Time (UTC+9) is set for 135°E, while Seoul sits near 127°E. Korean readers often correct the birth time for longitude, which can move a birth near an hour boundary into a different hour pillar.

Lunar calendar. Korea and China each compute the lunar calendar in their own time zone, so a date can differ by one day. Lunar New Year 2027 is February 7, 2027 in Korea and February 6, 2027 in China. Pillars follow the solar terms, so this matters only when converting a lunar birthday.

The late 子 hour. For births between 23:00 and midnight, some teachers switch to the next day’s pillar and some keep the same day. Both views exist in Korea and in China.

Emphasis. Popular Korean readings lean on 10-year luck cycles, compatibility (gunghap, 궁합) and plain life advice, and use folk terms such as samjae. Chinese-language readings more often sit next to Tai Sui (太歲) customs and feng shui. These are habits, and teachers vary more than countries do.

Saju vs Western astrology

Western astrology places the sun, moon and planets in 12 zodiac signs and 12 houses at the moment of birth. Saju uses no planet positions. The sun appears only indirectly, through the solar terms that set the year and month.

Your Chinese zodiac animal is just the branch of your year pillar. It is not the same idea as a Western sun sign, which depends on your birth month.

How SajuBunny does it

SajuBunny follows Korean practice: solar terms are calculated to the minute, the longitude correction is on by default, births from 23:00 use the next day’s pillar by default (you can switch), and lunar dates use the Korean calendar by default.