TL;DR:
Convert every person's working hours to UTC, then look for the hours they share.
Sometimes there is no shared hour. Then someone stretches their day, and the burden should rotate.
Create the event in one time zone and let each calendar show it in the viewer's own zone.
You need one call with people in New York, London and Singapore. Asking "what time suits you?" in a group thread produces a dozen messages and a wrong guess about daylight saving. A calmer method is to put everyone on one clock, find the overlap, and then check the result with a person.
Use UTC as the common clock
UTC is a reference time that does not change with the seasons. Each place is described as an offset from it, such as UTC−5 or UTC+8. If you convert everyone's hours to UTC, comparing them is just comparing numbers.
Offsets are not fixed for places that use daylight saving time. New York is UTC−5 in winter and UTC−4 in summer. London is UTC+0 in winter and UTC+1 in summer. Singapore stays at UTC+8 all year. The switch dates differ between the United States and the United Kingdom, so for a few weeks each spring and autumn the gap between New York and London is not what you expect. Always check the offsets for the actual date of the meeting.
Before you start
Ask each person for their normal working hours, not just their city. Nine to five is an assumption.
Pick the exact date, since offsets depend on it.
Check each invitee's calendar time zone settings are right. A laptop that travelled can leave a calendar on the wrong zone.
Decide how long the meeting is and whether it can be recorded or shared in writing for people who cannot attend.
Step by step
List each person's hours in local time: For example, 9:00 to 17:00 for everyone.
Convert the start and end to UTC: Subtract the offset: local time minus the offset gives UTC. For UTC−5, add 5 hours. For UTC+8, subtract 8.
Find the overlap: The shared window starts at the latest start and ends at the earliest end.
Check the window is not empty: If the latest start is after the earliest end, there is no shared hour.
Convert the chosen time back for each person: Write it in every local time in the invite so nobody has to calculate.
Create the event once: Use one time zone for the event, and let each calendar display it in the viewer's zone.
Worked example: a meeting for New York, London and Singapore
Date: a Thursday in mid-November, when New York is on winter time (UTC−5), London is UTC+0 and Singapore is UTC+8. Everyone works 9:00 to 17:00.
City | Offset | Working hours in UTC |
|---|---|---|
New York | UTC−5 | 14:00 to 22:00 |
London | UTC+0 | 09:00 to 17:00 |
Singapore | UTC+8 | 01:00 to 09:00 |
Check each row. New York: 9 + 5 = 14 and 17 + 5 = 22. London needs no change. Singapore: 9 − 8 = 1 and 17 − 8 = 9.
The latest start is 14:00 (New York) and the earliest end is 09:00 (Singapore). Since 14:00 is after 09:00, all three cities share no working hour at all. Any pair works though: New York and London overlap from 14:00 to 17:00 UTC, which is 3 hours. London and Singapore only touch at 09:00, so they share nothing.
So someone has to stretch. Say you choose 13:00 UTC for 45 minutes. That is 8:00 in New York (13 − 5), 13:00 in London and 21:00 in Singapore (13 + 8). It is early for one person and late for another, and London gets an easy afternoon. This is a cost, so say it out loud in the invite, and rotate the inconvenient slot between regions on later meetings so the same people do not always pay.
Note: Write the time in the invite as: Thu 13:00 UTC, 8:00 New York, 13:00 London, 21:00 Singapore. Anyone can verify it in ten seconds.
Setting up the event
Create the event in your calendar and set its time zone to one you are sure of, or to UTC if the app allows. Add the invitees. Each person's calendar shows the event in their own zone because the app stores the moment in time, not the clock face. Then look at your own calendar's time zone settings and the invitees' reported availability, if your app shows it, before you send.
Mistakes to avoid
Using a city name and no date. The offset depends on the season.
Forgetting that Singapore does not change clocks while New York and London do, so the gap moves twice a year.
Always picking the slot that suits your own team.
Writing "EST" or "PST" when you mean "Eastern time". In summer the zone name changes.
Not repeating the converted times in the invite text.
Doing it faster
DuckyHelper can read the offsets you wrote down on your screen when you press the key, and double-check the arithmetic out loud. Verify the daylight saving dates against your calendar app anyway.
Frequently asked questions
What is UTC?
A standard reference time that does not shift with the seasons. Other times are written as plus or minus hours from it.
Why does the gap between two cities change?
Because places switch to and from daylight saving time on different dates, or not at all.
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