Calendar applications handle timezones automatically. This is both a blessing and a curse. When it works, events appear at the correct local time for each attendee. When it fails, meetings are missed and confusion follows.
How Calendar Timezone Conversion Works
When you create an event:
- The calendar app stores the event in your current timezone (or a timezone you specify)
- When another user views the event, it converts to their timezone
- DST changes are handled based on the timezone rules at the event's date
This usually works. But problems arise in several scenarios.
The Travelling Organiser Problem
You create a recurring weekly meeting while in London. You then travel to New York. The meeting was created in London time, so it stays at that time — which may now be inconvenient for you.
Worse, if you edit the meeting while in New York, some calendar applications will reinterpret the time in your new timezone, shifting all future occurrences.
The DST Shift Problem
You schedule a meeting for “9am London time” with a colleague in New York. In winter, London is GMT (UTC+0) and New York is EST (UTC-5), so the meeting is at 4am New York time — probably not what you intended, but at least consistent.
In March, the US shifts to daylight saving before the UK does. For three weeks, the offset between London and New York changes from 5 hours to 4 hours. The meeting time shifts for the New York attendee.
Best Practices
1. Use UTC for Internal Anchoring
For recurring meetings that span multiple timezones, consider anchoring to UTC. “This meeting occurs at 14:00 UTC every Tuesday” is unambiguous and will not shift with DST.
2. Include Multiple Timezones in the Description
In the event description, list the local time for each major attendee group:
Weekly Sync — 14:00 UTC / 9am New York / 2pm London / 10pm Singapore
3. Review Recurring Events Quarterly
DST transitions happen in March/April and October/November. Review your recurring meetings after each transition to ensure they still occur at sensible times for all attendees.
Key Advice
Calendar apps hide complexity. This is usually good, but it means you cannot see when something will go wrong until it does. Be proactive about DST transitions and timezone changes.