Korean Daylight Time (KDT)

UTC offset: +10:00 (historical, summer only)
Standard offset: +09:00 (KST, year-round)
IANA identifier: Asia/Seoul
Abbreviation: KDT (no longer active)
DST status: Discontinued (last observed 1988)

Korean Daylight Time advanced South Korea's clocks one hour from KST (UTC+09:00) to UTC+10:00 during summer. The practice was used most recently in 1987 and 1988, tied to the 1988 Seoul Olympics (the government wanted to align Korean business hours more closely with Japan and with global broadcasting schedules for the Games).

After the Olympics ended, DST was abandoned. South Korea has remained on KST (UTC+09:00) permanently since then. North Korea also does not observe DST (and used UTC+08:30 briefly from 2015-2018 before reverting to +09:00 to match the South).

Why Korea Rejected DST

Work culture: Like Japan, South Korea has notoriously long working hours. An extra hour of daylight wouldn't translate to earlier departures. Hweshik (mandatory after-work drinking/dining) culture means many workers are out past midnight regardless of sunset.

Air conditioning: Korean summers are hot and humid (monsoon season, July-August). Extended evening daylight means extended heat exposure. Energy savings from reduced lighting are offset by increased AC usage.

Japan alignment: South Korea's largest trading partner and closest time-zone neighbor is Japan (also +09:00, no DST). Misalignment would complicate cross-border business.

Public ambivalence: Periodic government proposals to reinstate DST (most recently around 2008-2009, citing energy savings) have been met with public indifference or opposition.

South Korea Today

At permanent KST (UTC+09:00), South Korea runs on an efficient, highly scheduled society. Trains run on time. Business hours are precise. The country's tech sector (Samsung, SK, LG, Hyundai) operates globally but anchors to KST.

Seoul (~9.7 million, metro ~26 million): one of the world's largest metropolitan areas. Gangnam, Hongdae, Myeongdong, and the Yeouido financial district operate at all hours. Convenience stores are open 24/7. PC bangs (gaming cafes), noraebang (karaoke rooms), and jjimjilbangs (bathhouses) serve night owls.

The 1988 Olympics DST experiment is now a footnote. Most Koreans under 40 have no memory of clock changes.

What KDT Would Mean Today

If Korea observed DST at +10:00:

• Mismatch with Japan (no DST, permanent +09:00)
• Same offset as eastern Australia (AEST)
• Extended evening light (sunset around 8:30 PM in Seoul, June)
• Very early sunrise (around 4:30 AM)

The business case for aligning with AEST is weak. The argument for not misaligning with Japan is strong.

Technical Identifiers

• Asia/Seoul (IANA canonical)
• KDT (historical summer abbreviation)
• KST (current permanent abbreviation)
• Windows: "Korea Standard Time"
• DST last observed: 1988

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