What about births overseas?

The correction works the same way, using the difference between that country's standard meridian and the birthplace's longitude. Choose the country and city from the birthplace list and the historical daylight saving and standard time changes of that time zone are applied automatically; if your birthplace is not listed, choose a nearby city in the same time zone.

Calculation Standards

Why does Saju correct for the birthplace's local mean time, and why subtract 32 minutes for Seoul?

As of 2026-10-24 · Edited by Sajunyang · about 1700 characters

One-line answer

The Hour Pillar in Saju is set by the position of the sun (solar time), not by the clock. Korea Standard Time is based on 135°E (Akashi, Japan), but Seoul sits at 126.98°E, so the sun rises later by a longitude difference of about 8 degrees × 4 minutes = about 32 minutes. A birth in Seoul therefore needs about 32 minutes subtracted from clock time to get actual solar time, and quite a few people's hour branch changes with this correction.

How is local mean time calculated?

The Earth turns 360 degrees in 24 hours, so each degree of longitude is a difference of 4 minutes. Subtract the birthplace's longitude from the 135° standard meridian and multiply by 4 minutes to get the correction. Seoul at 126.98° is (135 − 126.98) × 4 ≈ 32 minutes; Busan at 129.08° is about 24 minutes; Gwangju at 126.85° about 33 minutes; and Gangneung at 128.90° about 24 minutes. Choose your birth city on Sajunyang and it calculates this automatically from that city's longitude.

Strictly speaking, there is also the equation of time (up to ±16 minutes), by which the sun runs fast or slow with the season, and some schools use 'true solar time', but most almanacs use 'local mean time', which corrects for longitude only. Sajunyang also uses local mean time.

Does a 32-minute difference change the chart?

Because the Hour Pillar changes every two hours, people born within the last 32 minutes of each block (roughly 1 in 4) have their hour branch pulled one step earlier. For example, a birth at 1:15 p.m. by the clock looks like the Mi hour (1 to 3 p.m.), but in local mean time it is 12:43 p.m., the O hour (11 a.m. to 1 p.m.). A birth at 11:15 p.m. becomes 10:43 p.m. in local mean time, the Hae hour rather than the Rat hour, and the Day Pillar stays on the same day.

FAQ

What about births overseas?: The correction works the same way, using the difference between that country's standard meridian and the birthplace's longitude. Choose the country and city from the birthplace list and the historical daylight saving and standard time changes of that time zone are applied automatically; if your birthplace is not listed, choose a nearby city in the same time zone.

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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.