What Is Saju? The Korean Four Pillars, Explained

Saju (사주) is the Korean name for the Four Pillars of Destiny — the full form is saju-palja (사주팔자, 四柱八字, "four pillars and eight characters"). It is not a rival system that happened to reach the same answers. It is the same system, transmitted from Tang and Song China through Goryeo and Joseon, running on the same sexagenary cycle and agreeing with BaZi on the two points that trip everyone up: the year begins at 立春 / 입춘, and the day master is the centre of the reading.

So if a saju tool and a BaZi tool hand you different charts for the same birth, the disagreement is almost never about the system. It is about which clock the birth time was read from.

What saju means, word by word

The technical discipline in Korea is called myeongrihak (명리학, 命理學) — the study of the logic of destiny. Its terms are the Chinese ones, pronounced in Korean:

Korean	Hanja	What it is
사주 saju	四柱	The four pillars
사주팔자 saju-palja	四柱八字	The four pillars and eight characters
천간 cheongan / 지지 jiji	天干 / 地支	Heavenly stems / earthly branches
오행 ohaeng	五行	The five elements
일간 ilgan	日干	The day master — the reference point of the chart
십신 sipsin	十神	The ten gods
용신 yongsin	用神	The useful god
대운 daeun / 세운 seun	大運 / 歲運	Luck pillars / the annual pillar
궁합 gunghap	宮合	Compatibility between two charts
입춘 ipchun	立春	Beginning of spring — the year boundary
절기 jeolgi	節氣	The solar terms

Korean readings are usually quoted by the day stem — "I'm an 甲木 day master" — which is the same anchor we build the ten gods around. Compatibility worked the same way in practice: a groom's family sent the birth data (사주단자) and a reader assessed 궁합 before a betrothal. Under the Joseon court, calendar and fate work was administered by a royal bureau (관상감) and examined in the state's own tests, so the discipline was institutional rather than folk.

Is saju the same as BaZi?

Structurally, yes — and "BaZi vs saju" is therefore a slightly misleading thing to search for. There is no rivalry to resolve. Both systems build the same four pillars from the same sexagenary cycle, read the same hidden stems, name the same ten gods (십신 / 十神), pick a useful god (용신 / 用神) by the same logic, and run the same ten-year luck pillars (대운 / 大運). A chart for the same moment, on the same time basis, comes out the same on either side.

That leaves two real differences, and neither is about the system:

1. Vocabulary. Korean practitioners use the Chinese terms pronounced in Korean, which is why a reading sounds unfamiliar even when the mechanics are identical.
2. The clock. The birth time each tradition feeds in comes from a different national clock history. This one genuinely changes charts, and it is the rest of this article.

The year boundary is the same — and it is not Lunar New Year

Both traditions date the year from 立春 / 입춘, the astronomical instant around 3–5 February, and both treat the lunar new year as the boundary of the folk zodiac rather than of the pillars. Korean teachers spend a lot of energy telling clients that their chart does not change on 설날, for exactly the reason we explain to readers born between the two dates. If you were born in the gap, the animal you grew up with and the year branch in your chart differ — the stems and branches reference shows both calendars, and what BaZi is covers the boundary rules.

One genuine divergence inside the system, shared by both traditions rather than separating them: how to handle a birth between 23:00 and midnight. Some schools advance the day pillar at 23:00, others keep it on the civil date and only change the hour stem. We publish which convention we use and apply it consistently, which is the only useful thing a calculator can do here.

Where Korean saju really differs: the clock

Here is the part that is genuinely Korean, and it is a matter of civil law rather than of astrology. Korea has not always run on the same clock:

Period	Offset	Standard meridian
1 April 1908 – 31 December 1911	UTC+8:30	127°30′E
1 January 1912 – 20 March 1954	UTC+9	135°E
21 March 1954 – 9 August 1961	UTC+8:30	127°30′E
10 August 1961 – present	UTC+9	135°E

On top of that, Korea has observed daylight saving in 1948–1951, 1955–1960 and 1987–1988, an hour ahead of the offset in force for part of each year.

This is why Korean practitioners traditionally subtract 30 minutes from the recorded birth time. It is not a rounding of Seoul's longitude: 135° mean minus 127°30′ is 7.5°, and 7.5° × 4 minutes is exactly 30 minutes. The constant is the gap between Korea's current standard meridian and the one the country used from 1908–1911 and again from 1954–1961. Whether or not the convention descends from that history, that is the number it corresponds to.

Two things follow that the constant cannot cover.

The correction is not the same everywhere in Korea. The exact meridian term depends on the birth longitude, so the same rule gives different answers in different cities:

Birthplace	Longitude	Meridian term
Seoul	126.98°E	−32.1 min
Busan	129.08°E	−23.7 min
Mokpo	126.38°E	−34.5 min

It ignores the equation of time. The sun is not exactly on your meridian at noon, and the gap swings from about −14 minutes in mid-February to about +16 minutes in early November. The 30-minute rule says nothing about the season, so it is roughly right in spring and autumn and off by half an hour in late winter.

A worked example

Take a birth on 4 February 1990 at 07:31 in Seoul — the same civil date as the worked example used across this site, but placed one hour from an hour-pillar boundary.

Basis	Local time used	Hour branch	Hour pillar
Clock as recorded	07:31	辰時 (07:00–09:00)	庚辰
Traditional −30 minutes	07:01	辰時	庚辰
Exact: meridian −32.09 + equation of time −13.48	06:45:25	卯時 (05:00–07:00)	己卯

The clock reading and the traditional correction agree; the exact correction does not, because the total is −45.6 minutes, not −30. Same city, same minute, one pillar apart — and the year, month and day pillars are untouched in all three rows, which is the point: only the hour is in play.

Two more checks make the shape of it clear.

• Season changes the answer. The same Seoul birth time on 3 November 1990 gives an equation of time of +16.4 minutes, a net correction of −15.7, and a true solar time of 07:15 — still 辰時, agreeing with the raw clock.
• Era changes the answer too. On 10 March 1958, Seoul's standard meridian was still 127°30′E, so the meridian term was only −2.1 minutes: the corrected time is 07:17:41 and the hour branch stays 辰時. A birth from that era needs almost no meridian correction at all, while a birth in the DST windows of 1948–1951, 1955–1960 or 1987–1988 needs an hour removed as well as the meridian term.

You can run any of these yourself on the true solar time page, which prints each correction term separately so the arithmetic can be checked instead of trusted — or on the saju calculator, which is the same engine reading the same four pillars under the Korean name.

What this means if you are Korean or Korean-diaspora

Use the system you find readable — they are the same system, so there is no loss either way. Two practical notes, both about the clock rather than the chart:

• Give the recorded wall-clock time and the city, not a pre-corrected time. If you were born during a daylight-saving window, say so; an hour is the difference between one hour pillar and the next.
• If you were born between 1954 and 1961, expect the meridian term to be small. Korea's clocks were closer to the peninsula's own meridian in that period than they are today.

And if a tool asks only for "time" with no city and no era handling, treat the hour pillar it gives you as provisional. Not because the system is unreliable, but because the input was.

Common questions

What is saju?

Saju (사주) is the Korean name for the Four Pillars of Destiny — the Chinese system that reads a person's chart from the year, month, day and hour of birth, each written as a pair of a heavenly stem and an earthly branch. The longer form saju-palja (사주팔자, 四柱八字) means "four pillars and eight characters", counting the eight stem-and-branch characters those four pairs produce.

Is saju the same as BaZi?

Structurally yes: same sexagenary cycle, same 立春 year boundary, same day master, same ten gods, useful god and luck pillars, same 10-year rhythm. The differences are vocabulary and the clock conventions of the country you were born in. A chart for the same moment and the same time basis comes out the same.

Why do Korean readings subtract 30 minutes from the birth time?

Because Korea's clock runs on the 135°E meridian while the peninsula sits around 127.5°E. The 30 minutes is exactly the difference between those two meridians — 7.5° × 4 minutes. The exact correction varies with the birth longitude and with the season, so it is a convenient constant rather than a precise one.

I was born in Korea in the 1980s. Does the clock history affect my chart?

Only if you were born inside a daylight-saving window — 1987 and 1988, from the second Sunday in May to the second Sunday in October. Outside those windows your clock was already on standard time. If you were born inside one, the recorded time is an hour ahead of standard time and that hour has to come off before any pillar is computed.

Does the zodiac animal change between saju and BaZi?

No. Both use the lunar new year for the popular zodiac and 立春 for the year pillar, so a Korean and a Chinese reader will give you the same animal — and both may give you a different animal from your year branch if you were born between the two dates.

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Whichever name you use for it, the eight characters are the same computation. To see the rules and the correction terms printed on a birth you can check, calculate your chart or read the conventions we apply.