How should an event's time zone be expressed in structured data?

Definition: An event date-time should include a numeric UTC or GMT offset when the local clock time is known. For an event date-time without an offset, Google uses the time zone of the event's location.

Key facts

• Google's Event structured data documentation says to specify a time zone with the UTC or GMT offset in startDate, endDate, or previousStartDate.
• The same documentation gives 2019-09-05T19:00:00-05:00 and 2019-09-05T19:00:00-04:00 as examples for a 7pm event in New York under different daylight saving conditions.
• When no time zone is provided, Google uses the time zone of the event's location in location.
• A date-only value such as 2019-07-10 represents the date regardless of the time zone, while a date-time without an offset such as 2019-07-20T00:00:00 means midnight in the event's time zone.
• RFC 3339 defines numeric offsets as local time minus UTC and gives 18:50:00-04:00 as the same time as 22:50:00Z.

Which value should a website publish?

Schema.org's Event definition describes an event as happening at a certain time and location. Its startDate property is a date and time in ISO 8601 date format, and endDate uses the same date format. Google's Event documentation was last updated on 8 September 2026 and recommends including the appropriate UTC offset when an event starts at a specific local hour.

For a known local time, the structured value can therefore retain the local clock and add its numeric offset:

"startDate": "2019-09-05T19:00:00-05:00"

RFC 3339 describes its Internet format as a profile of ISO 8601 and defines a full date-time as a full date, the letter T, and a full time. The time offset is either Z or a numeric hour and minute offset such as -05:00.

What does the offset mean?

RFC 3339 defines a numeric offset as the local time minus UTC. A negative offset means that the local clock is behind UTC, so 18:50:00-04:00 corresponds to 22:50:00Z. The offset expresses the relationship for that date-time; it does not replace the event's location data.

Google's New York example shows why the offset belongs in the value: the page gives GMT/UTC-5 for standard time and GMT/UTC-4 for daylight saving time. The offset in the data should match the local time rule that applies to the event date.

What happens when the value has no zone?

Google states that an offset-free date-time is interpreted using the time zone of the event's location. Its example 2019-07-20T00:00:00 means midnight on that date in the time zone where the event happens, and the documentation calls this likely wrong when the event was not intended to start at midnight.

The location also affects how Google interprets a value that already has an offset when the page illustrates a UTC instant. For 2019-08-15T00:00:00+00:00, Google gives 2019-08-14T17:00:00-07:00 when the location is California and 2019-08-15T09:00:00 when the location is Korea. A date-only value is different: Google's 2019-07-10 example means the event starts sometime in that calendar day at its location when used as startDate, and ends sometime in that day when used as endDate.

Related terms

• Structured data
• JSON-LD
• How do I mark an online event's attendance mode and location?

FAQ

Should you use Z for every event?

No. Use Z when the value is expressed in UTC. For a local event time, use the numeric offset that applies to that date, such as -05:00 or -04:00 in Google's New York examples.

What should you publish when only the event date is known?

Use a date-only value such as 2019-07-10. Google documents this as a date regardless of the time zone and distinguishes it from an offset-free midnight date-time.

Does location still matter when the date-time has an offset?

Yes. Schema.org defines an Event in terms of time and location, and Google's interpretation examples vary by the location supplied for the event.

Sources

1. Google Search Central, "Event structured data", 2026-09-08
2. Schema.org, "Event", 2026-09-16
3. RFC Editor, "RFC 3339: Date and Time on the Internet: Timestamps", July 2002

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