Calculation Standards
Does daylight saving time affect Saju? Why do people born in 1987–1988 need to recheck their Hour Pillar?
As of · Edited by Sajunyang · about 2000 characters
One-line answer
Korea observed daylight saving time in 1948–1951, 1955–1960 and 1987–1988, moving clocks forward one hour, and standard time itself changed to UTC+8:30 in 1908, UTC+9 in 1912, UTC+8:30 in 1954 and UTC+9 in 1961. For people born in those periods, the clock time on the birth record differs from actual solar time by 1 hour to 1 hour 30 minutes, so without correction the Hour Pillar is wrong, and if the birth was near the Rat hour, the Day Pillar is wrong too.
When did Korea observe daylight saving time?
① Each year from 1948 to 1951, spring through autumn (roughly May to September); ② each year from 1955 to 1960, spring through autumn; ③ May 10 to October 11, 1987 and May 8 to October 9, 1988 (around the Seoul Olympics). During those periods the clock ran one hour ahead of real time, so a birth recorded at 2 p.m. was 1 p.m. in standard time.
There were standard time changes as well. On April 1, 1908, the Korean Empire adopted UTC+8:30 based on 127.5°E; on January 1, 1912, the Japanese colonial government changed it to Japan Standard Time, UTC+9; on March 21, 1954, it reverted to UTC+8:30; and on August 10, 1961, it became UTC+9 again, which is still in use. For those born in 1954–1961, the clock itself ran on a basis 30 minutes behind today's.
What goes wrong without correction?
Because the Hour Pillar runs in two-hour blocks, a one-hour difference changes the hour branch half the time. For example, a birth in Seoul at 2:30 p.m. on July 15, 1988 becomes 1:30 p.m. after removing daylight saving time, and 12:58 p.m. after subtracting local mean time (−32 minutes), which is the O hour rather than the Mi hour. For a birth around 11 p.m. to midnight, whether it falls in the Rat hour changes, and so does the Day Pillar. The Hour Pillar is where the details of children, later life and career are read, so if it is wrong, every reading in that area is off.
Sajunyang converts the entered time to UTC using the historical rules of the IANA time zone database (Asia/Seoul) and then calculates solar time from the birthplace's longitude, so you only need to enter the clock time at the moment of birth as it was.
Periods that need Saju time correction
| Period | What was different | Correction |
|---|---|---|
| 1908.4.1 ~ 1911.12.31 | Standard time UTC+8:30 | +30 minutes relative to today |
| Summers of 1948–1951 and 1955–1960 | Daylight saving time | −1 hour |
| 1954.3.21 ~ 1961.8.9 | Standard time UTC+8:30 | +30 minutes relative to today |
| 1987.5.10~10.11 · 1988.5.8~10.9 | Daylight saving time | −1 hour |
| All periods · Seoul | Longitude gap from the 135°E standard meridian | About −32 minutes (varies by city) |
FAQ
- What if the birth record is already written in standard time?
- Hospital birth certificates record the clock time of the day. During daylight saving periods the clock time itself was moved forward, so enter it as it is and leave the correction to us.
- I was born in 1988 but in winter. Does it matter?
- Daylight saving time was in effect only from May to October, so births in other months get no daylight saving correction, only the local mean time correction.
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This article is reference material summarizing traditional Saju theory and does not replace medical, legal or investment judgment. Our calculation standards are published at About Sajunyang.