Should the organiser use their own city as the event zone?

Use the city where the decision-makers sit, or the city named in the agenda. Consistency matters more than which side you pick, as long as the zone id is real.

What if a guest’s phone is set to the wrong zone?

The invite still carries the instant. Their phone will show the wrong wall time until they fix Settings. Putting both city times in the body is the backup.

Is “9am my time” ever acceptable?

Only in a thread where everyone already knows the city. It is not acceptable in a calendar object that will be forwarded.

How to write a timezone-safe calendar invite

Most broken meetings are not math errors. They are invitations that stored a wall clock without a zone, or used an abbreviation that means three places at once.

Last updated 2026-08-20 · Written by the NowZones publisher in Denmark. Offsets and DST examples use the IANA Time Zone Database via the same libraries as the city clocks. This is editorial explanation, not legal, medical, or aviation advice.

Store one instant, display many clocks

A good invite is a single instant in UTC, shown as local time to each attendee. Google Calendar and Outlook do this when you pick a time zone for the event. They fail when you type “9am EST” into the title and let everyone interpret EST themselves.

Prefer the city: “09:00 in New York (America/New_York).” If the other side is in London, add “14:00 in London” in the description so a screenshot still makes sense when the calendar UI hides the zone.

Do not set the event in UTC unless every attendee lives in aviation. Humans read city names. UTC belongs in the footer for the people who want it.

Ban ambiguous abbreviations

CST is Central Standard Time in the US, China Standard Time, and Cuba Standard Time. IST is India and Irish Summer Time. BST is British Summer Time and Bangladesh Standard Time. If you must write an abbreviation, pair it with a city or an IANA id.

EST is only correct in US winter. From March to November the east coast is EDT. Writing EST in July is a classic off-by-one.

The IANA id is ugly in a customer email and perfect in a calendar. Use both: friendly city in the subject, America/New_York on the event.

Recurring series and DST

A weekly series that crosses a spring-forward will skip or repeat an hour on one side if the software stored a floating local time. Test the first instance after the US March change and after the EU March change — they are different weeks.

If half the attendees do not observe DST (India, China, most of Africa), the gap to London or New York will jump even when “nothing happened” on their side. Say that in the invite once so nobody “fixes” it.

When in doubt, convert 09:00 on the NowZones converter for the actual date, then paste both results into the description.

Try the tools

Frequently asked questions

Should the organiser use their own city as the event zone?: Use the city where the decision-makers sit, or the city named in the agenda. Consistency matters more than which side you pick, as long as the zone id is real.
What if a guest’s phone is set to the wrong zone?: The invite still carries the instant. Their phone will show the wrong wall time until they fix Settings. Putting both city times in the body is the backup.
Is “9am my time” ever acceptable?: Only in a thread where everyone already knows the city. It is not acceptable in a calendar object that will be forwarded.