London is 9 hours behind Seoul in winter (KST UTC+9 → GMT UTC+0) and 8 hours behind in summer (KST UTC+9 → BST UTC+1). A 9:00 AM start in Seoul is 12:00 AM GMT in winter and 1:00 AM BST in summer in London. Best meeting window — Winter (KST): 6:00 PM – 9:00 PM KST (9:00 AM – 12:00 PM GMT); Summer (KST): 4:30 PM – 7:30 PM KST (8:30 AM – 11:30 AM BST).
With a 9 hours gap in Winter (KST) (KST → GMT) and a 8 hours gap in Summer (KST) (KST → BST), Seoul and London have 0 hours of simultaneous 9:00 AM – 5:00 PM business hours in either season. Meetings use morning and early-evening shoulder windows within 7:00 AM – 9:00 PM local time.
Optimal Seoul–London shoulder bridge for Winter (KST) (9 hours gap) and Summer (KST) (8 hours gap), ending at or before 9:00 PM local time.
Covers every hour where Seoul or London is outside 7:00 AM – 9:00 PM local time (19h/day in Winter (KST); 18h/day in Summer (KST)).
| Seoul Time | London (Winter (KST → GMT)) | Day Shift | London (Summer (KST → BST)) | Call Status |
|---|---|---|---|---|
| 9:00 AM KST (Morning Start) | 12:00 AM GMT | Same day | 1:00 AM BST | Overnight / Rest |
| 12:00 PM KST (Midday / Noon) | 3:00 AM GMT | Same day | 4:00 AM BST | Overnight / Rest |
| 3:00 PM KST (Afternoon) | 6:00 AM GMT | Same day | 7:00 AM BST | Overnight / Rest |
| 6:00 PM KST (Evening Wrap-up) | 9:00 AM GMT | Same day | 10:00 AM BST | Shoulder Hours |
| Seoul (KST) | London (Winter (KST → GMT)) | Day (London) | London (Summer (KST → BST)) | Availability (Seoul ↔ London) |
|---|---|---|---|---|
| 12:00 AM KST in Seoul | 3:00 PM GMT in London | -1 day | 4:00 PM BST (-1 day) | Seoul–London Overnight |
| 1:00 AM KST in Seoul | 4:00 PM GMT in London | -1 day | 5:00 PM BST (-1 day) | Seoul–London Overnight |
| 2:00 AM KST in Seoul | 5:00 PM GMT in London | -1 day | 6:00 PM BST (-1 day) | Seoul–London Overnight |
| 3:00 AM KST in Seoul | 6:00 PM GMT in London | -1 day | 7:00 PM BST (-1 day) | Seoul–London Overnight |
| 4:00 AM KST in Seoul | 7:00 PM GMT in London | -1 day | 8:00 PM BST (-1 day) | Seoul–London Overnight |
| 5:00 AM KST in Seoul | 8:00 PM GMT in London | -1 day | 9:00 PM BST (-1 day) | Seoul–London Overnight |
| 6:00 AM KST in Seoul | 9:00 PM GMT in London | -1 day | 10:00 PM BST (-1 day) | Seoul–London Overnight |
| 7:00 AM KST in Seoul | 10:00 PM GMT in London | -1 day | 11:00 PM BST (-1 day) | Seoul–London Late evening / night |
| 8:00 AM KST in Seoul | 11:00 PM GMT in London | -1 day | 12:00 AM BST | Seoul–London Late evening / night |
| 9:00 AM KST in Seoul | 12:00 AM GMT in London | Same day | 1:00 AM BST | Seoul–London Overnight |
| 10:00 AM KST in Seoul | 1:00 AM GMT in London | Same day | 2:00 AM BST | Seoul–London Overnight |
| 11:00 AM KST in Seoul | 2:00 AM GMT in London | Same day | 3:00 AM BST | Seoul–London Overnight |
| 12:00 PM KST in Seoul | 3:00 AM GMT in London | Same day | 4:00 AM BST | Seoul–London Overnight |
| 1:00 PM KST in Seoul | 4:00 AM GMT in London | Same day | 5:00 AM BST | Seoul–London Overnight |
| 2:00 PM KST in Seoul | 5:00 AM GMT in London | Same day | 6:00 AM BST | Seoul–London Overnight |
| 3:00 PM KST in Seoul | 6:00 AM GMT in London | Same day | 7:00 AM BST | Seoul–London Overnight |
| 4:00 PM KST in Seoul | 7:00 AM GMT in London | Same day | 8:00 AM BST | Seoul–London Shoulder |
| 5:00 PM KST in Seoul | 8:00 AM GMT in London | Same day | 9:00 AM BST | Seoul–London Shoulder |
| 6:00 PM KST in Seoul | 9:00 AM GMT in London | Same day | 10:00 AM BST | Seoul–London Shoulder |
| 7:00 PM KST in Seoul | 10:00 AM GMT in London | Same day | 11:00 AM BST | Seoul–London Shoulder |
| 8:00 PM KST in Seoul | 11:00 AM GMT in London | Same day | 12:00 PM BST | Seoul–London Shoulder |
| 9:00 PM KST in Seoul | 12:00 PM GMT in London | Same day | 1:00 PM BST | Seoul–London Late evening / night |
| 10:00 PM KST in Seoul | 1:00 PM GMT in London | Same day | 2:00 PM BST | Seoul–London Late evening / night |
| 11:00 PM KST in Seoul | 2:00 PM GMT in London | Same day | 3:00 PM BST | Seoul–London Late evening / night |
Between Seoul (South Korea, Asia/Seoul) and London (United Kingdom, Europe/London), the seasonal offset shifts by 1 hour. In winter standard time (KST vs. GMT), London (UTC+0) is 9 hours behind Seoul (UTC+9). In summer (KST vs. BST), London (UTC+1) is 8 hours behind Seoul (UTC+9).
No Daylight Saving Time observed. Remains on KST (UTC+9) year-round.
| Date Window | Duration | Active Zones | Time Difference | Regime |
|---|---|---|---|---|
| Since Oct 25, 2026 | 154 days | KST (UTC+9) → GMT (UTC+0) | 9 hours | Standard Alignment (Active Now) |
| Mar 28, 2027 – Oct 31, 2027 | 217 days | KST (UTC+9) → BST (UTC+1) | 8 hours | Standard Alignment |
| Oct 31, 2027 – Nov 3, 2027 | 3 days | KST (UTC+9) → GMT (UTC+0) | 9 hours | Standard Alignment |
Because London is 9 hours behind Seoul in winter and 8 hours behind in summer, London remains on the previous calendar day (-1 day) from 12:00 AM until 9:00 AM KST in winter (8:00 AM KST in summer) in Seoul. During those hours, Mon–Fri in Seoul maps to Sun–Thu in London (and Tue–Sat in Seoul maps to Mon–Fri in London). After 9:00 AM KST (8:00 AM KST in summer), both locations share the same weekday.
Weekend & Workday Alignment: Monday morning in Seoul (before 9:00 AM KST / 8:00 AM KST in summer) lands on Sunday in London—which is London's weekend (Sat–Sun). Likewise, Friday afternoon/evening in London corresponds to Saturday morning in Seoul (Seoul's Sat–Sun weekend). Morning calls in Seoul should be scheduled Tuesday–Friday in Seoul (which is Monday–Thursday afternoon/evening in London).
Geographically, Seoul (South Korea, 37.57°N, 126.98°E, IATA: ICN) and London (United Kingdom, 51.51°N, 0.13°W, IATA: LHR/LGW/STN) are separated by a great-circle distance of 8,857 km (5,503 miles, approximately 11h non-stop flight). By longitude, true solar time in London is 8 hours and 28 minutes behind Seoul (a 32-minute divergence from the 9 hours standard civil clock offset): Seoul (37.57°N, 126.98°E) sits 8.02° west of the 135.0°E KST reference meridian, so mean solar noon occurs at 12:32 PM KST year-round, while London (51.51°N, 0.13°W) sits 0.13° west of the 0.0°E GMT reference meridian, so mean solar noon occurs at 12:01 PM GMT in winter and 1:01 PM BST in summer.
For Seoul → London: Literal BST (British Summer Time) is UTC+1, active in the UK from the last Sunday of March to the last Sunday of October. In winter, the UK returns to GMT (UTC+0).
| Abbreviation Meaning | UTC Offset | IANA Zone | Major Cities & Regions |
|---|---|---|---|
| British Summer Time Primary Here | UTC+1 (late March – late October) | Europe/London | Active on Seoul → London: London, Manchester, Edinburgh, Belfast |
| Bangladesh Standard Time | UTC+6 (year-round) | Asia/Dhaka | Not used for Seoul → London: Dhaka, Chittagong (Bangladesh) |
In winter (standard time), London (GMT, UTC+0) is 9 hours behind Seoul (KST, UTC+9). In summer (daylight saving time), London (BST, UTC+1) is 8 hours behind Seoul (KST, UTC+9).
4:00 PM in Seoul corresponds to 7:00 AM GMT (same day) in winter and 8:00 AM BST (same day) in summer in London, placing it inside waking hours (7:00 AM – 9:00 PM) in both cities.
In winter (KST), the best window is 6:00 PM – 9:00 PM KST in Seoul (9:00 AM – 12:00 PM GMT in London). In summer (KST), use 4:30 PM – 7:30 PM KST in Seoul (8:30 AM – 11:30 AM BST in London). Avoid hours outside 7:00 AM – 9:00 PM local time (9:00 PM – 4:00 PM KST (+1 day) in winter; 9:00 PM – 3:00 PM KST (+1 day) in summer).
Seoul: No DST (KST year-round). London: Sun, Mar 28, 2027 (GMT → BST, new gap: 8 hours (BST UTC+1 vs KST UTC+9)).
In winter (KST), 9:00 AM Seoul is 12:00 AM GMT and 12:00 PM is 3:00 AM GMT in London. In summer (KST), 9:00 AM is 1:00 AM BST and 12:00 PM is 4:00 AM BST.