How should an event with an unknown start time be marked?

Definition: Use a date-only startDate value when an event date is known but its start hour is unknown. Google says to omit a granular hour rather than insert midnight or another time that the event information does not establish.

Key facts

• Google's Event structured data documentation applies its date and time guidance to startDate, endDate, and previousStartDate.
• When the start hour is unknown, Google says to omit a granular hour and gives 2019-08-15 as an example for both startDate and endDate.
• Schema.org defines startDate on Event as accepting Date or DateTime, and describes it as the item's start date and time in ISO 8601 date format.
• Schema.org defines Date as a date value in ISO 8601 date format, which supports a date-only value for the date portion of an event.

What does a date-only value mean?

A date-only value contains the calendar date and no hour, minute, or offset. Google's interpretation table says that 2019-07-10 means the date regardless of the timezone. Used in startDate, it means the event starts at some time during that day in the event location. The value therefore records the known date while leaving the start hour unspecified.

"startDate": "2019-07-10"

Schema.org's Date type describes this kind of value as an ISO 8601 date. Its Event page also lists Date and DateTime as the expected types for startDate, so a date-only value is part of the vocabulary rather than an empty placeholder.

What should be left out?

Leave out a granular time when the source information does not give one. Google explicitly says, “If you don't know the hour for the start time, don't specify a granular hour.” Its recommended example is "startDate": "2025-07-21"; the page marks "startDate": "2019-08-15T00:00:00+00:00" as not recommended for this situation. A midnight timestamp states a specific hour, so it changes an unknown value into an unsupported event detail.

If the event lasts across several dates and the times are unknown, Google says to indicate both the start and end date and to leave out the time. For an event that happens all day, the documentation likewise says to omit a granular hour and gives the same date-only form for both properties.

How should the markup be checked?

Inspect the JSON-LD or other structured data on the event page. When the start hour is unknown, the startDate value should use the date-only form shown below, with no T00:00:00 suffix and no offset invented for midnight.

{
  "@type": "Event",
  "startDate": "2019-08-15",
  "endDate": "2019-08-15"
}

Google lists startDate among the required properties for its event structured data, while endDate is listed as recommended. The page also says that each event must accurately describe its name, start date, and location. Compare the date in the markup with the event information published on the page before validation. If a real start hour is later published, replace the date-only value with that accurate local time and the appropriate UTC offset, following Google's date and time guidance.

Related terms

• Structured data
• JSON-LD
• Article update dates

FAQ

Should an unknown start time be encoded as midnight?

No. Google's event guidance marks a midnight timestamp as not recommended when the start hour is unknown and recommends a date-only startDate instead.

Does a date-only value mean that the event starts at midnight?

No. Google explains that a date-only startDate means the event starts sometime during that date in its location. Midnight is a separate, specific time value.

What should happen when the start hour becomes known?

Update startDate with the documented date and local start time, including the appropriate UTC offset when applicable. Google's example for a specified local hour uses 2019-07-20T17:00:00 and an offset for California.

Sources

1. Google Search Central, "Event (Event) structured data", 8 September 2026
2. Schema.org, "Event", August 2026
3. Schema.org, "Date", August 2026

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