Saju vs BaZi: Korean and Chinese Four Pillars Compared
If you have read BaZi books in English or used a Chinese Four Pillars calculator, you may wonder whether Korean saju is a separate system, and whether it will hand you a different chart. The short answer: it is the same system, built on the same astronomy, and for most people it produces exactly the same eight characters. The differences sit in vocabulary, in a few calculation conventions that matter only at the edges, in Korea's clock and calendar history, and in what people use the chart for.
Neither tradition is "the accurate one." Both descend from the same classics, and practitioners in each country argue among themselves about the points below.
One system, two vocabularies
The Four Pillars took shape in China. The method that makes the day stem the center of the chart is traditionally credited to Xu Ziping (徐子平) of the Song dynasty and is still called the Ziping method. It spread to Korea, and to Japan, where it is known as shichū suimei (四柱推命). Korean students still learn from the Chinese classics, such as the Ziping Zhenquan (子平眞詮, Korean Japyeong jinjeon), the Qiongtong Baojian (窮通寶鑑, Gungtong bogam) and the Ditian Sui (滴天髓, Jeokcheonsu). What changes from one language to the other is pronunciation and, sometimes, the preferred word.
| Concept | Korean | Chinese | Characters |
|---|---|---|---|
| Four pillars | saju 사주 | sizhu | 四柱 |
| Eight characters | palja 팔자 | bazi | 八字 |
| The discipline | myeongrihak 명리학 | mingli | 命理 |
| Day Master | ilgan 일간 | rigan, also rizhu | 日干, 日主 |
| Five elements | ohaeng 오행 | wuxing | 五行 |
| Ten Gods | sipseong 십성 or sipsin 십신 | shishen | 十星, 十神 |
| Hidden stems | jijanggan 지장간 | canggan | 支藏干, 藏干 |
| Luck pillars | daeun 대운 | dayun | 大運 |
| Useful god | yongsin 용신 | yongshen | 用神 |
| Solar terms | jeolgi 절기 | jieqi | 節氣 |
| Start of Spring | Ipchun 입춘 | Lichun | 立春 |
| Marriage compatibility | gunghap 궁합 | hehun | 宮合, 合婚 |
The stems and branches change sound as well. 甲 is jia in Mandarin and gap in Korean, 子 is zi and ja, so the first pair of the sixty is Jia Zi in a BaZi book and gapja (갑자) in Korea. Korean texts also keep the traditional character forms, 大運 and 沖, where mainland Chinese books print the simplified 大运 and 冲. Sajucheop's English pages use pinyin, since that is what English-language BaZi literature uses, and give the Korean reading alongside.
| Stem | Pinyin | Korean | Element |
|---|---|---|---|
| 甲 | Jia | gap 갑 | Yang Wood |
| 乙 | Yi | eul 을 | Yin Wood |
| 丙 | Bing | byeong 병 | Yang Fire |
| 丁 | Ding | jeong 정 | Yin Fire |
| 戊 | Wu | mu 무 | Yang Earth |
| 己 | Ji | gi 기 | Yin Earth |
| 庚 | Geng | gyeong 경 | Yang Metal |
| 辛 | Xin | sin 신 | Yin Metal |
| 壬 | Ren | im 임 | Yang Water |
| 癸 | Gui | gye 계 | Yin Water |
Two traps catch people moving between the systems. In Korean, sin names both the stem 辛 and the Monkey branch 申, which pinyin keeps apart as Xin and Shen. In pinyin, Wu is both the stem 戊 and the Horse branch 午, which Korean keeps apart as mu and o.
The year starts at the Start of Spring, in both traditions
A common belief holds that Korean saju starts the year at Ipchun while Chinese BaZi starts it at Lunar New Year. That is not quite right. Classical BaZi and Korean saju both change the year pillar at Lichun, or Ipchun, the moment the sun reaches 315 degrees of celestial longitude, around February 4. What follows Lunar New Year is the popular zodiac: Chinese New Year celebrations mark the arrival of the new animal, and in everyday Korean conversation many people also count their animal (tti, 띠) from Seollal (설날), the Korean Lunar New Year.
So when two sources disagree about the animal of someone born in late January or early February, the split is usually between a practitioner's chart and a zodiac table, not between Korea and China. The Ipchun guide works through the 2027 case hour by hour.
The clock problem: true solar time
The hour pillar follows the sun, not the clock, and here Korea's geography stands out. Korea Standard Time, UTC+9, is set to the 135°E meridian, which runs through western Japan, while Seoul lies at about 127°E. At four minutes per degree, a Seoul clock runs about 32 minutes ahead of the sun. Chinese practitioners apply the same correction under the name zhen taiyang shi (真太陽時); it simply plays out differently because China keeps a single time zone, UTC+8, for the whole country.
| City | Longitude | Standard time | Clock vs. sun |
|---|---|---|---|
| Seoul | 127.0°E | UTC+9 | about 32 min fast |
| Busan | 129.1°E | UTC+9 | about 24 min fast |
| Tokyo | 139.7°E | UTC+9 | about 19 min slow |
| Beijing | 116.4°E | UTC+8 | about 14 min fast |
| Shanghai | 121.5°E | UTC+8 | about 6 min slow |
| Ürümqi | 87.6°E | UTC+8 | about 2 h 10 min fast |
Korea's clock history adds a second layer. The country used UTC+8:30 from 1908 to 1911, moved to UTC+9 in 1912, returned to UTC+8:30 from March 21, 1954 to August 9, 1961, and has used UTC+9 since. It also ran summer time in 1948–1951, 1955–1960 and 1987–1988. Ignore that history and the hour pillars of people born in those years can shift, one reason a parent's chart may differ between Korean sites.
Sajucheop's Korean calculator applies the Seoul correction of −32 minutes by default, with a switch to turn it off, handles both UTC+8:30 periods automatically, and warns about summer-time years. During 1954–1961 the correction shrinks to about two minutes, because UTC+8:30 is set to 127.5°E, almost exactly Seoul's longitude. The English calculator asks for your birthplace's time zone and works from clock time, so if you were born within about half an hour of the start of a two-hour block, read the hour pillar on both sides of the line. Strictly speaking, astronomers' true solar time also includes the equation of time, a seasonal wobble of up to about a quarter of an hour; Sajucheop applies the longitude part, and some practitioners add the seasonal part too.
The late-night Rat hour
The Rat hour runs from 11 p.m. to 1 a.m. by the sun, so it straddles midnight, and the tradition has never settled which day its first half belongs to. One school changes the day at 11 p.m. (jasi ilbyeon, 자시일변, 子時日變). The other, the late-Rat or yajasi (야자시, 夜子時) convention, keeps the day pillar until midnight but gives the hour pillar the next day's Rat hour. Both exist in Chinese and Korean practice. Sajucheop follows the late-Rat convention; other calculators may use either or let you choose.
The two schools agree on the hour pillar and disagree on the day pillar, and since the day stem is the Day Master, the stakes are high. Take a birth in Seoul at 11:40 p.m. on September 13, 2026. After the solar correction it is about 11:08 p.m., inside the Rat hour.
| Convention | Day pillar | Hour pillar | Day Master |
|---|---|---|---|
| Late Rat (Sajucheop) | 庚寅 Geng Yin | 戊子 Wu Zi | Yang Metal |
| Day changes at 11 p.m. | 辛卯 Xin Mao | 戊子 Wu Zi | Yin Metal |
Combined with the Seoul correction, the late-Rat window on a Seoul clock runs from about 11:32 p.m. to 12:32 a.m., so a baby born at 12:20 a.m. still takes the previous day's pillar. If you were born between 11 p.m. and 1 a.m., find out which rule your calculator uses and read both day pillars.
Two lunar calendars, a day apart
The traditional lunisolar calendar starts each month on the day of the new moon, and which day that is depends on the time zone. China computes its calendar for UTC+8. Korea's calendar, published by the Korea Astronomy and Space Science Institute (KASI), is computed for Korean time. When a new moon falls in the last hour before midnight in China, it is already the next day in Korea, and the month begins a day later there.
That is exactly what happens at the start of 2027. The new moon arrives at 11:56 p.m. on February 6, China time, which is 12:56 a.m. on February 7 in Seoul. Chinese New Year 2027 is February 6; Seollal is February 7. The same split happens again in 2028 (January 26 in China, January 27 in Korea), and according to the calendar data Sajucheop uses, it last happened in 1997.
The pillars themselves never use the lunar calendar: years and months follow the solar terms, and days follow the unbroken sixty-day count. The lunar calendar matters for one practical reason. Many Korean families still keep birthdays by the lunar calendar (eumnyeok saengil, 음력 생일), and a lunar date converted with a Chinese table in one of the split months lands on the wrong solar day, which means the wrong day pillar. Convert a Korean lunar birthday with Korean (KASI) calendar data.
What Korea uses the chart for
The biggest differences are cultural. Chinese-speaking communities have their own customs, such as marriage matching (hehun, 合婚) and date selection with almanacs like the Tung Shing (通勝) of Hong Kong. In Korea, the same stems and branches feed a distinct set of practices.
- Gunghap (궁합), compatibility. Couple readings are historically tied to marriage negotiations, when the groom's family sent a saju danja (사주단자), a folded paper bearing his four pillars, to the bride's family. Korean gunghap pays special attention to wonjin (원진, 怨嗔), six branch pairs said to breed resentment without an obvious cause: Rat and Goat, Ox and Horse, Tiger and Rooster, Rabbit and Monkey, Dragon and Pig, Snake and Dog.
- Jakmyeong (작명), naming. Naming offices choose hanja whose element fills a gap in the baby's chart, and check stroke counts and the elements of the name's sounds.
- Taekil (택일), date selection. Wedding, moving and opening dates are chosen against the charts involved, often combined with folk customs like son eomneun nal (손없는날), the lunar days ending in 9 or 0 that are considered safe for moving house.
- Tojeong bigyeol (토정비결, 土亭祕訣). A New Year fortune book traditionally attributed to the Joseon scholar Yi Ji-ham, whose pen name was Tojeong. It is not saju: it uses your age and lunar birth month and day to pick one of 144 readings for the year.
- Samjae (삼재, 三災). A folk belief that each group of three zodiac animals passes through three years of caution every twelve years.
Korean popular fortune content also leans heavily on named markers called sinsal (신살, 神殺), such as dohwasal (도화살, 桃花殺), the "peach blossom" star of charm and attraction. Chinese BaZi uses the same markers under the name shensha (神煞). The peach blossom guide covers the best known of them.
Will a Korean calculator give you a different chart?
Usually not. For most birth data, a careful Chinese calculator and a careful Korean one produce identical eight characters. Look more closely if any of these apply to you:
- You were born within a couple of hours of a solar term, so your month pillar, or at Ipchun your year pillar, depends on minutes.
- You were born near the start of a two-hour block, where the solar-time correction can move the hour pillar.
- You were born between 11 p.m. and 1 a.m., where the Rat hour convention can move the day pillar.
- You were born in Korea in the UTC+8:30 years or in a summer-time year.
- Your birth date was converted from a lunar date with a non-Korean table.
Interpretation varies more, but as much inside each country as between them: readers everywhere differ on how to judge strength and which useful god to choose.
To see your chart computed the Korean way, with astronomically computed solar terms and the late-Rat rule, cast it on Sajucheop. Then compare your day pair with the 60 Day Pillars, where every page gives the pinyin and Korean names side by side, or see how the popular Lunar New Year boundary works on the zodiac finder.
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