Birth Time and Place in Saju: Why They Change Your Chart

Your birth time sets the hour pillar, which changes every two hours, so it supplies two of the eight characters in a Saju chart. Your birth place matters because Saju uses local solar time, which can differ from clock time by half an hour or more depending on longitude and daylight-saving history. If you don't know your birth time you still get three pillars and your Day Master, and the calendar itself follows the solar terms, so the Saju year begins at Ipchun around February 4.

Why birth time matters

The day is divided into twelve two-hour blocks, each named for an Earthly Branch. The Rat (子 Ja) hour runs from 23:00 to 01:00, the Ox (丑 Chuk) from 01:00 to 03:00, and so on around the clock. The hour branch, together with a stem that follows from the day stem, forms the hour pillar (시주 時柱 siju).

The hour pillar adds two characters to the chart. That can change the element balance, add or remove a Ten God, and supply a root that makes the Day Master stronger or weaker. Traditionally it is also associated with children, later life and long-term outcomes.

Birth time can matter beyond the hour pillar. Near midnight it can decide which day you were born on, and therefore your Day Master. Near a solar term it can decide your month pillar, and near Ipchun even your year pillar. It also fixes the starting age of your luck pillars, which is counted from your exact birth moment to the nearest solar term.

The midnight question

Schools disagree on when the day changes. One common approach changes the day at 23:00, the start of the Rat hour. Another splits the Rat hour at midnight, treating 23:00 to 00:00 as the "late Rat hour" (야자시 夜子時 yajasi) of the old day and 00:00 to 01:00 as the "early Rat hour" (조자시 朝子時 jojasi) of the new day. Both views have long-standing supporters in Korea. If you were born between 23:00 and 01:00 local solar time, it is worth knowing which convention a reading uses.

If you don't know your birth time

Many people don't know their exact birth time, and that is fine. Without it you still have:

• the year pillar,
• the month pillar, which sets the season and is among the most important factors in the chart,
• the day pillar, including your Day Master.

That is six of eight characters, enough for a meaningful reading of temperament, element balance and most Ten Gods relationships. Orienteller supports charts without a birth time and reads them as three-pillar charts rather than guessing an hour. The luck pillar starting age can still be estimated, with a margin of error of a few months.

If your time is approximate, such as "morning" or "around 3 p.m.," it may still fall clearly inside one two-hour block. If it sits close to a boundary, a reader may compare both possible hour pillars. Some practitioners try to work out an unknown hour from life events, a process known as rectification; treat that as speculative.

Why birth place matters

Saju divides the day by the Sun, not by the clock. Clock time is set for a whole time zone, but solar time depends on longitude. The correction from clock time to local solar time has three parts.

1. Longitude. Each degree of longitude is four minutes of time. Korea Standard Time (UTC+9) is set at 135°E, while Seoul sits at about 127°E, so Seoul's local mean solar time runs about 32 minutes behind the clock. Busan, further east, is about 24 minutes behind.
2. Daylight saving and zone history. Many countries have changed their time zones or used daylight saving in some years. South Korea observed summer time in several periods, including 1987 and 1988, and used UTC+8:30 for some years in the 1950s and early 1960s. A birth recorded on the clock during those periods needs a different correction.
3. The equation of time. The real Sun runs up to about 16 minutes ahead of or behind the average Sun over the course of a year. Correcting for it gives true (apparent) solar time.

The equation of time is left out of the table for simplicity. Without these corrections, a Seoul birth at 13:20 would be cast in the Goat hour instead of the Horse hour. Whether to apply the equation of time on top of the longitude correction is debated; some practitioners use mean solar time only. Orienteller uses your birthplace's longitude and its time-zone and daylight-saving history to compute true local solar time.

The Saju calendar: Ipchun and the solar terms

The Saju year begins at 입춘 (立春 Ipchun, "start of spring"), the solar term that falls around February 4. It does not start on January 1 or on Lunar New Year, which moves between late January and mid-February. Someone born on January 25, 2026, belongs to the previous Saju year, 乙巳 Eul-sa. Someone born on February 10, 2026, belongs to 丙午 Byeong-o, even though Lunar New Year that year falls on February 17.

Months follow the same logic. There are 24 solar terms (절기 節氣 jeolgi), set every 15 degrees of the Sun's path along the ecliptic, and twelve of them (the 절 jeol terms) start the Saju months. The Tiger month begins at Ipchun, the Rabbit month at 경칩 (驚蟄 Gyeongchip) around March 6, and so on. Lunar calendar months are not used to set the month pillar.

Because solar terms fall at a precise moment, a birth on the day of a term can belong to either month depending on the hour. Orienteller computes each solar term from the Sun's actual position. You can try this with the free calculator: enter your date and, optionally, your time and place to find your Day Pillar and see all four pillars. Nothing is stored. For a broader introduction, see what Saju is.

FAQ

What if I don't know my birth time for Saju?

You still get the year, month and day pillars, including your Day Master, which is six of the eight characters. Orienteller reads charts without a birth time as three-pillar charts rather than guessing the hour.

Why does my birthplace affect my Saju chart?

Saju uses local solar time rather than clock time. Your birthplace's longitude and its daylight-saving history determine how far clock time differs from solar time, which can change the hour pillar and, near midnight, the day pillar.

When does the Saju year start?

The Saju year starts at Ipchun, the start-of-spring solar term around February 4. It does not start on January 1 or on Lunar New Year.

Does Saju use the lunar calendar?

Saju pillars are set by the solar terms, which follow the Sun. A lunar birth date can be converted to find the right pillars, but the month and year boundaries come from the solar terms, not from lunar months.

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