Scheduling a call across time zones with Korea

Korea is UTC+9 and doesn't use daylight saving. That one fact covers most of it. The two things that still catch people are the DST switch on your side, and the half-hour zones.

The moment it matters is when someone sends Mon 9:00 AM PST and you have to figure out what that is in Seoul. Get it wrong and a meeting simply doesn't happen.

The rough shape

The two numbers in each row are the next section.

Daylight saving is where everyone slips

The US and Europe move their clocks forward an hour in summer, so the gap to Seoul changes by an hour depending on the season.

• New York: 13 hours in summer, 14 in winter
• London: 8 hours in summer, 9 in winter

Korea does not observe DST, so the Seoul clock never moves. Only your side does.

The more annoying part is that the changeover dates differ. The US starts on the second Sunday in March and ends on the first Sunday in November; Europe starts on the last Sunday in March and ends on the last Sunday in October. For those two or three weeks in between, even the US–Europe gap is not what it usually is.

So don't do this in your head, particularly in March and late October.

What to actually write in the invitation

Put the date in. "9am" on its own leaves open which day's 9am it is. With Seoul the gap is more than half a day, so converting frequently rolls the date over.

Bad:    See you Tuesday at 9am
Better: Tue Mar 4, 11:00 AM EST = Wed Mar 5, 1:00 AM KST

Write both zones and the other person can check your arithmetic. Write one and somebody has to convert, and the one converting is the one who gets it wrong.

The overlap is narrower than you think

Taking normal working hours (9am to 6pm) on both sides:

• London 9–10am in London is 5–6pm in Seoul. About an hour of genuine overlap
• New York no overlap at all. One side is early morning or late evening
• Los Angeles worse still. There is no hour that is reasonable on both sides

So a call with either US coast starts as a question of who takes the inconvenience. Around 8am Seoul (7pm New York) or 11pm Seoul (10am New York) are the realistic slots.

What this does not cover

• Half-hour and 45-minute zones: India is UTC+5:30, which is 3 hours 30 minutes from Seoul. Nepal is UTC+5:45
• Countries with several zones: the mainland US has four, Australia three
• Times on flight tickets: an arrival time is always local to where you land

New York, London, Tokyo and Los Angeles run side by side in the clock box, each row carrying its current time and its gap from Seoul.

Daylight saving is handled for you. The browser works out each city's zone itself, so nothing needs touching when the clocks change in March.

Open the calendar beside it to watch the date roll over. Write the meeting into the schedule box and a reminder arrives when the hour comes.

→ See what time it is in New York