Korea's Clock Changes and Your Birth Time: Standard Time and Daylight Saving Time

Korea's Clock Changes and Your Birth Time: Standard Time and Daylight Saving Time

If you were born in Korea in the 1950s or in 1987 or 1988, the time on your birth record may not mean what it means today. Korea's standard time sat at UTC+8:30 from March 21, 1954 to August 9, 1961 (UTC+9 again from August 10), and the country used daylight saving time (called summer time in Korea) in several years, including 1987 and 1988. A saju (Korean four-pillar astrology) chart is built from the moment you were born, so a clock time from those years usually needs one or two adjustments in our method before the hour pillar is drawn. This guide describes the records and our approach for curiosity and reflection; it is not a prediction.

Why a clock time is not the same as a birth moment

A clock shows an agreed time, not the position of the sun. The Encyclopedia of Korean Culture puts it simply: noon in local mean time is when the average sun crosses the meridian, and each 15 degrees of longitude adds up to 60 minutes of difference. Countries pick one standard meridian so that a whole region can share one clock.

Today Korea uses the 135 degrees east meridian, which is nine hours ahead of world time. Seoul, however, sits near 127 degrees east. The same entry notes that Seoul's local mean time differs from Korean standard time by about 32 minutes.

Our calculator reads saju hours by the sun, not the clock: it takes out daylight saving time and applies a longitude correction (our own rule; see How We Calculate). A birth record gives clock time. In our method, turning that clock time into a sun-based time is the key step, and the rules for doing it depend on what the clock meant on your birth day.

Korea's standard time over the 20th century

Korea's clocks have moved more than once. Here are the changes we could confirm in official or encyclopedia records:

Period (24-hour clock)Standard meridianOffset from world timeRecord
Before March 21, 1954Not covered hereNot covered hereThe encyclopedia says Korea matched Japan's time before 1954 (earlier changes not covered here)
March 21, 1954 to August 9, 1961127 degrees 30 minutes eastUTC+8:30Presidential Decree No. 876, in force March 21, 1954
From August 10, 1961135 degrees eastUTC+9Act No. 676: from August 10, 1961, 00:00 became 00:30

The 1954 rule is listed in the Korean law archive as a presidential decree that took effect on March 21, 1954. The encyclopedia explains why it did not last: a half-hour offset made conversion to world time awkward, and time math was a hassle for travelers moving often between Seoul, Tokyo and Okinawa. The 1961 law then set the 135 degrees east meridian again, and its text says that on August 10, 1961, midnight was turned into 12:30 a.m. In other words, half an hour of clock time on that night was skipped.

The encyclopedia states that on April 1, 1904, Korean clocks were moved so that 11 o'clock became noon, to remove the time gap with Japan.

The Standard Time Act passed in 1986 (as enacted) keeps the 135 degrees east meridian and allows a presidential decree to shift the clock for part of the year for daylight saving time.

Daylight saving time: the extra hour on the clock

Daylight saving time means moving the clock one hour ahead for part of the year. The two encyclopedia entries we opened give slightly different start dates, so we show both:

  • The entry on time systems says what it calls summer time was used in 1948 to 1951, in 1955 to 1960, and in 1987 and 1988, each time by moving the clock one hour ahead.
  • The entry on daylight saving time says a presidential decree started it in April 1949, that it ran with adjusted periods until 1960, and that it was ended by a cabinet order on May 1, 1961. It adds that Korea brought it back in 1987 ahead of hosting the 1988 Olympics, partly to line up with the time zones of major partners such as the United States, and dropped it again in 1989.

For saju, the practical point is the same either way. If daylight saving time was in force on your birth day in one of those years, your clock showed one hour more than standard time. The sun did not move; the clock did.

How our calculator handles it

Our How We Calculate page covers this in two steps.

Step 1: convert the clock time to a single universal moment (section 1). You enter the birth date, hour and minute as the clock showed them, and choose your birth city. Using the international time zone database (IANA), we look up what that clock meant on that exact day, including daylight saving time, and convert your birth to one moment in Coordinated Universal Time (UTC). The page says it plainly: from 1954 to 1961, Korea's standard time was UTC+8:30, not UTC+9, and Korea used daylight saving time in several years, including 1987 and 1988; the time zone database includes these changes. If a clock time did not exist (skipped when daylight saving time began) or happened twice (when it ended), your result tells you which reading we used.

Step 2: adjust for the sun (section 3). For your day and hour pillars, we first take out daylight saving time, because it is a clock rule, not a change in the sun. Then, by default, we apply a longitude correction (our own rule): minutes = (city longitude minus the time zone's standard meridian) times 4. For UTC+9 the meridian is 135 degrees east; for UTC+8:30 (Korea, 1954 to 1961) it is 127.5 degrees east.

Two short examples, using a Seoul birth and that formula:

  • A January 1958 birth at 9:20 a.m. Korea was on UTC+8:30, so the meridian is 127.5 degrees east. Seoul is about half a degree west of it, so the correction is about 2 minutes, and the chart reads about 9:18 a.m. If someone wrongly assumed UTC+9, they would subtract about 32 minutes and get about 8:48 a.m. That is a difference of about 30 minutes, enough to move a birth near an hour boundary into a different hour block.
  • A July 1987 birth at 8:10 a.m., for a day when daylight saving time was in force. We first take off the hour to get 7:10 a.m. standard time, then subtract about 32 minutes for Seoul's longitude, for about 6:38 a.m. Skipping the daylight saving step would put the reading a full hour later.

The longitude correction changes your day and hour pillars. Your year and month pillars come from the UTC moment in step 1, so getting the offset right matters there too, mostly for births close to a solar term (the start of a saju month). Your result shows the corrected time we used, so you can check it.

What to do with an old birth record

Enter the time exactly as written on the record or as your family remembers it, and pick Seoul or the nearest listed city. Please avoid subtracting the daylight saving hour or the half hour yourself; the calculator does that, and doing it twice would shift your hour. If your birth is close to the start of an hour, the corrected time shown with your result will tell you which hour it fell in.

Ready to try it? Open the free saju calculator and look for the corrected time line in your result.

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