Which zone this page means. MST is standard time only; MDT (UTC-6) applies from March to November. Arizona stays on MST all year. South Korea does not observe daylight saving, so KST applies all year. It shares an offset with Japan.
MST is behind KST by 15 hours today
On 19 August 2026, Mountain Standard Time is on MDT at UTC-06:00 and Korea Standard Time is on KST at UTC+09:00. The gap between them is 15 hours, with KST ahead. So 9:00 am in MST is 12:00 am in KST, and 5:00 pm in MST is 8:00 am in KST. Going the other way, see KST to MST.
The gap is not constant, and that is the part that catches people out
Mountain Standard Time is currently observing daylight saving and changes next on 1 November 2026, when clocks go back an hour. Korea Standard Time does not observe daylight saving at all, so the whole of the seasonal change comes from the MST side: the gap moves by an hour twice a year even though nothing changes in Korea Standard Time.
When you can actually both be at work
Taking a working day as 9:00 am to 5:00 pm local at each end, there are 0 overlapping hours in a normal day. There is none: the two working days do not touch at all, so any live meeting between Mountain Standard Time and Korea Standard Time has to sit outside somebody's normal hours. The table above shows which end has the shorter stretch to give up.
Zone rules are set by legislation and change, sometimes at short notice. This page is built against tzdata 2026a, last reviewed 2026-08-18. Quarterly. Zone rules change by legislation, sometimes at short notice. Version and review date are shown on every zone page. The converter above reads your browser's own copy of the zone database, so if a rule has changed since this page was built the live answer follows the new rule.
Every convention used above — whether the start date counts, how month ends are clamped, which holidays close an office — is written out on the methodology page, including the daylight-saving rules behind the 15-hour gap above.