Born during daylight saving time

Your birth record shows what the clocks read at the time, daylight saving included. Enter that time as it is. From your birth date and birthplace we work out whether daylight saving was in force, and if it was, we take the shift back off to reach the standard time of the day. If you subtract the hour yourself first, it can come off twice.

Daylight saving only covered part of each year it was used. A Korean birth in January or December 1988, for instance, isn't affected at all. The table below gives the exact dates for Korea.

Korean standard time itself has moved, separately from daylight saving. In 1948–1951 and 1987–1988 it was UTC+9, set to 135°E, so summer clocks read UTC+10. In 1955–1960 standard time was UTC+8:30, set to 127.5°E, so summer clocks read UTC+9:30. The switch to UTC+8:30 on March 21, 1954 changed standard time itself rather than starting daylight saving, so no hour is taken off for it.

Where the clocks went back at 00:00, they returned to 23:00 the evening before. For 1948 we follow the original decree and end it at 24:00 on September 22 (we used the IANA date, September 13, until we checked the decree), as our calculation guide explains.

1. If the time falls in daylight saving, we take off the shift (one hour in Korea) to reach standard time.
2. With the True Solar Time Adjustment on, we move it again by (birthplace longitude − standard-time meridian) × 4 minutes plus the equation of time for that date. The meridian comes from standard time, not the summer clock, so the hour isn't counted twice.
3. The result sets your hour pillar, and also decides whether a late-evening birth falls in the Zi hour.
4. Your year and month pillars skip this adjustment and compare your actual moment of birth with the solar term. Leave the summer hour in and that moment is an hour out, which can change the year or month pillar for a birth within an hour of a solar term.

The formula and how births outside Korea are handled are covered in the true solar time section of our calculation guide.

For births in Seoul we use Seoul City Hall, at 126.98°E. Against a 135°E meridian its longitude part is 32 minutes; against 127.5°E, 2 minutes. With the adjustment on, the equation of time for the date is added, between about −14 and +16 minutes. Add the daylight saving hour and the total taken off the recorded time depends on the period.

With the adjustment on, add that day's equation of time to the "adjustment on" total. In the 1948–1951 and 1987–1988 spans that puts it between about −99 and −79 minutes, depending on the date; in 1955–1960, between about −69 and −52.

Say you were born in Seoul at 12:00 on July 1, 1988. Taking off the summer hour gives 11:00 standard time. The adjustment then takes off 36 minutes, 32 for longitude and 4 for that day's equation of time, bringing it to 10:24. That is the Si hour (巳時), so the hour pillar is 乙巳 (Yi Si). With the adjustment off, 11:00 stays as it is, which is the Wu hour (午時), and the hour pillar becomes 丙午 (Bing Wu).

So for a Seoul birth during daylight saving in 1948–1951 or 1987–1988, a recorded time from an even hour to somewhere between 18 and 38 minutes past, depending on the date (12:00 to 12:35 on July 1, 1988), gets a different hour pillar depending on the adjustment alone. In 1955–1960 the longitude part is only 2 minutes, so the window sits within about 10 minutes before or after an even hour, depending on the date. The hour skipped on the first day of daylight saving is read as standard time, so it sits outside this pattern.

Switching the true solar time adjustment off removes both the longitude step and the equation of time. The daylight saving hour still comes off, because it corrects what the clocks actually read that day.

Some calculators make no adjustment, some adjust for longitude only, and some also add the equation of time, so if your hour pillar differs from another site's, match this setting first. AevoStar has both parts on by default, and you can turn the adjustment off under "See how this was calculated" on your result. Each time you switch it, we recalculate and show which pillars changed. There's no longitude-only setting; against such a calculator the gap is that day's equation of time.

On the day daylight saving began, an hour of clock time didn't exist: 02:00–02:59 on May 10, 1987, for example. On the day it ended, an hour ran twice, as 02:00–02:59 did on October 11, 1987. In 1948–1960 the skipped hour was 00:00–00:59 on the start date, and the repeated hour was 23:00–23:59 on the evening before the end date. We accept these times, and your calculation notes flag them as a daylight saving edge and say how they were read; the rule is in our calculation guide.

Elsewhere we read daylight saving from the IANA time zone history for your birthplace, and the longitude part of the adjustment is measured from the meridian of the standard time underneath, not from the summer clock. The same approach covers less common cases, such as the half-hour daylight saving on Lord Howe Island. Choosing your city, time zone history and dates that shift across time zones are covered in our guide to births outside Korea.

Without a time there's no hour pillar, so daylight saving can't move it. For a birth in Korea, the year and month pillars and the Luck Pillar starting age are read at noon standard time, and daylight saving isn't considered. Elsewhere we read noon on the local clock, with daylight saving applied if it was in force that day: a New York birth on May 15, 1990 is read at 12:00 EDT, which is 16:00 UTC.

Switch to the Detailed view and open "See how this was calculated" below your chart. For a daylight saving birth you'll see:

• Daylight saving time: that the summer hour was taken back, with the standard time it gave
• True solar time adjustment: how many minutes your birthplace and birth date moved the time (with the longitude part and the equation of time shown separately), and the time used for the hour pillar
• Standard time then in use: for births in Korea, shown when standard time was UTC+08:30, as in 1955–1960
• Daylight saving edge hour: shown only for a birth in a skipped or repeated hour

Daylight saving and the true solar time adjustment only move your moment of birth onto the clock used for the hour pillar; either way, the result is reference information drawn from traditional theory.