Why Calendar Invites Shift by 1 Hour During DST
Why Google Calendar, Outlook, and Apple Calendar meetings move when one country changes clocks before another. How to prevent scheduling bugs.
The short answer
Recurring calendar invites shift because calendar platforms store meetings tied to either a specific local timezone or a fixed UTC timestamp. When countries change clocks on different dates (such as the US starting DST 2–3 weeks earlier than Europe in March), the relative time difference between participants changes, forcing the meeting to shift by 1 hour for one of the parties.
The Root Cause: Local Time vs. UTC Anchors
When an organizer creates a recurring meeting at "10:00 AM Eastern Time", the calendar software calculates the UTC timestamp based on New York's current UTC offset.
| Calendar Event Anchor | What Happens During DST Change | Best Use Case |
|---|---|---|
| Organizer's Local Time (e.g., 10 AM ET) | Stays at 10 AM for US organizer; shifts from 3 PM to 4 PM for UK attendees | Internal company meetings where organizer's working hours are fixed |
| Attendee's Local Time (e.g., 3 PM GMT) | Stays at 3 PM for UK attendee; shifts from 10 AM to 9 AM for US organizer | Client-facing meetings where client's convenience takes priority |
| Fixed UTC Time (e.g., 14:00 UTC) | Shifts by 1 hour for both parties whenever their local clock changes | International server maintenance or open-source community calls |
How to Prevent Calendar DST Conflicts
- Verify meeting times during March and October/November: Set calendar notifications during the 3-week transatlantic transition gap.
- Clarify timezone ownership: Explicitly state whether a recurring sync follows ET or GMT/CET in the calendar description.
- Use world clock widgets: Check current live offsets on your phone before sending international invites.
Timezone: World Clock Widget
A world clock, converter and live day/night map for iPhone — 325 cities, offline, no account.
Figures on this page are computed from the IANA time zone database. Last generated 2026-08-20.