Korean Standard Time (KST)
Korean Standard Time (KST) is UTC+9 — nine hours ahead of Coordinated Universal Time. South Korea observes this time year-round with no daylight saving time. The IANA identifier for Seoul is Asia/Seoul.
History of KST
Korea's time zone history is unusually complicated. During the Japanese colonial period (1910–1945), Korea used UTC+9, the same as Japan. After liberation, South Korea briefly used UTC+8:30 (1954–1961), then UTC+9 (1961–present). North Korea used UTC+9 until 2015, then briefly UTC+8:30 ("Pyongyang Time"), and reverted to UTC+9 in 2018.
Current Offsets from Major Cities
- Seoul to New York: −14 hours (winter), −13 hours (summer when US observes EDT)
- Seoul to London: −9 hours (winter), −8 hours (summer when UK observes BST)
- Seoul to Tokyo: 0 hours (same time zone)
- Seoul to Beijing/Shanghai: −1 hour
- Seoul to Sydney: +1 to +2 hours (varies with Australian DST)
- Seoul to Mumbai: −3:30 hours
Business Hours Overlap with Seoul
Seoul's business hours are typically 09:00–18:00 KST. Because KST has no DST, the offset is constant year-round, making long-term scheduling simpler. However, the 14-hour gap with New York means there is no overlap in normal business hours — a 9 PM call in New York reaches Seoul at 11 AM the next day.
Tech Industry Note
South Korea hosts major tech companies including Samsung and LG, making KST relevant to global developers and product teams. Servers operating in Seoul are often in the ap-northeast-2 (AWS) or similar cloud regions, which log timestamps in UTC but display in KST for local monitoring dashboards.
KST vs. JST
KST and JST (Japan Standard Time) are identical offsets — both UTC+9, both with no DST. Despite being the same clock time, they are maintained as separate IANA zones (Asia/Seoul and Asia/Tokyo) because the two countries have different historical DST records.