Asia/Seoul

TZ identifier and aliases

Asia/Seoul is the canonical identifier for South Korea's civil time. ROK (Republic of Korea) is an older name still pointing at the same rules but is a deprecated alias — use Asia/Seoul in new code.

UTC offset and DST rule

Asia/Seoul is +09:00 year-round with no daylight saving time. South Korea's last DST experiment ended in 1988, and it has kept a single fixed offset ever since — there's no seasonal clock change to account for in any system built against this zone.

Using it in cron, CI and Postgres

Set TZ=Asia/Seoul for a process that should schedule by South Korean local time. Postgres accepts it via SET TIME ZONE 'Asia/Seoul'; or the timezone setting. Because the offset never changes, a cron job's local-time schedule behaves identically every day of the year, with no DST boundary or skipped/duplicated local hour to account for — one of the simpler zones in this family for recurring scheduled work.

History and quirks

Korea's time zone history includes a politically loaded detour: under Japanese colonial rule the peninsula used +09:00 starting in 1912, but after liberation South Korea briefly shifted to +08:30 in 1954 as a symbolic break from the colonial-era standard, before reverting to +09:00 in 1961 for practical alignment with international shipping and aviation schedules, including US military coordination during the Korean War era. South Korea tried daylight saving twice more since — around the 1988 Seoul Olympics, largely to extend evening broadcast windows for international audiences — before dropping it again immediately after. The peninsula's two halves diverged again decades later: North Korea unilaterally shifted to +08:30 ("Pyongyang Time") in 2015 to mark 70 years since liberation from Japan, then reverted to +09:00 in 2018 as a gesture of reconciliation ahead of inter-Korean summits — a reminder that Asia/Seoul and North Korea's own zone have not always matched, even though they do today.

For any system tracking historical timestamps across that period, North Korea's zone is a genuinely separate tz database entry (Asia/Pyongyang), not merely a footnote — code that assumed the two Koreas always shared one offset would have computed the wrong local time for any North Korean timestamp between August 2015 and May 2018. South Korea's own DST reversals cluster around major international events more than energy policy, a pattern distinct from most other DST histories in this family, which more often cite electricity conservation as the primary justification. Asia/Seoul's current fixed +09:00 has now held for over three decades, making it one of the more stable zones in East Asia despite the peninsula's complicated 20th-century history.

Offsets and DST transitions on this page are computed from the IANA time zone database bundled with your browser; the rules described above were verified against tzdata 2026b when this page was published.