How to schedule a meeting across time zones
Find the overlap, write the time with a city name, and check the two or three weeks a year when the usual gap is wrong.
Most mistakes in cross-zone scheduling are not arithmetic errors. They come from writing a time ambiguously, from assuming the gap between two cities is constant, or from trying to find an hour that does not exist. The meeting planner lays the working day of each city side by side so the overlap is visible; this guide is the reasoning behind it.
Start from working hours, not offsets
The question is not “what is the difference between London and New York” but “which hours are inside the working day in both”. If both keep 9 to 5, the five-hour gap leaves a three-hour window: 14:00 to 17:00 in London, 09:00 to 12:00 in New York. Add a third city and the window shrinks or vanishes. London, New York and Singapore have no common hour at all within 9 to 5: 09:00 in Singapore is 01:00 in London and 20:00 the previous evening in New York. Someone has to meet outside their day, and the only fair question is who, and whether it rotates.
The combinations with no overlap
Two cities twelve or more hours apart share no working hour. Across the Pacific this is routine: San Francisco to Tokyo is 17 hours (16 in the northern summer), San Francisco to Sydney 19 hours in the northern winter and 17 in the northern summer. Recurring meetings across these gaps work best at the edges, around 08:00 for one side and 17:00 or 18:00 for the other, and they should alternate who takes the early slot. A fixed time that is always convenient for the head office is remembered by the other office for years.
Write the time so it cannot be misread
A time needs a place. “3 p.m.” is meaningless in an invitation that crosses zones; “3 p.m. EST” is usually wrong in summer, when the US east coast is on EDT; and “3 p.m. GMT” is wrong for London for seven months of the year. The reliable form is the time followed by a city, “15:00 London”, or a UTC time with a Z. Abbreviations are the weakest option because so many collide: CST is Central Standard Time in the United States, China Standard Time and Cuba Standard Time; IST is India, Israel and Ireland. The time zone database guide explains why the database itself names zones by city.
Give the time in every participant’s zone, in the invitation text as well as the calendar event. Calendar software converts correctly when the event carries a zone, but people read the message before they open the event, and a time stated once in the organiser’s zone is the one most often misread. The event time tool produces a list of local times for one instant that can be pasted into the message.
The weeks when the gap changes
Daylight saving starts and ends on different dates in different places, and for a few weeks each year the usual difference between two cities is an hour off. The United States changes on the second Sunday of March; Europe on the last Sunday of March. For those two or three weeks London is four hours ahead of New York instead of five, and a 15:00 London weekly call lands at 11:00 in New York rather than 10:00. In autumn the mismatch runs from the last Sunday of October to the first Sunday of November. The southern hemisphere changes in the opposite direction, so the gap between London and Sydney swings by two hours over the year, from 11 to 9, with 10 for a few weeks at each change.
A standing meeting is anchored in one zone, usually the organiser’s. During a mismatch week it moves for everyone else. The least painful policy is to decide in advance which city the meeting is anchored to, say so in the invitation, and expect it to shift for the others twice a year. The daylight saving tool shows the next change for any zone, so the shift can be announced the week before rather than discovered on the day.
Days that do not line up
Across a large gap the date differs too. 18:00 on Thursday in San Francisco is 11:00 on Friday in Tokyo. A meeting “on Friday” means different things on each side, and a deadline of “end of day Friday” can be twenty hours apart depending on whose Friday. State the date with the time, in the same zone, and for deadlines give the instant in UTC as well as the local time that matters.
Half-hour and quarter-hour zones
India is on UTC+05:30 and Nepal UTC+05:45, and a planner that steps through hours will put Mumbai at the wrong half hour. A 09:30 start in London is 15:00 in Mumbai; the half hours cancel, which is often convenient. The guide to fractional offsets lists the places this matters.
A checklist
Before sending an invitation: name a city with every time; include each participant’s local time in the text; check whether either side changes clocks between now and the meeting; confirm the date on both sides for gaps over ten hours; and if the meeting is recurring, say which city it is anchored to. None of this takes more than a minute with the planner open, and each item corresponds to a way the meeting has been missed before.
Sources
Frequently asked questions
What is the best time for a meeting between London and New York?
Between 14:00 and 17:00 London time, which is 09:00 to 12:00 in New York, when both are inside a 9-to-5 day. For two or three weeks in March and one in late October the gap is four hours rather than five, so check before a standing meeting.
Is there an hour that works for London, New York and Singapore?
Not within a 9-to-5 day in all three. 09:00 in Singapore is 01:00 in London and 20:00 the previous day in New York. One office has to meet early or late, and the fair arrangement is to rotate which.
Should I write EST or ET in an invitation?
Neither, ideally. Write the time with a city, such as 10:00 New York, so that daylight saving is handled by whoever converts it. EST is wrong for the US east coast from March to November.
Why did my weekly transatlantic meeting move by an hour?
Because the US and Europe change clocks on different dates. Between the second Sunday of March and the last Sunday of March, and between the last Sunday of October and the first Sunday of November, the usual gap is an hour smaller.