Microsoft Graph all-day events return incorrect UTC start/end – organizer timezone not available

Question

Microsoft Graph all-day events return incorrect UTC start/end – organizer timezone not available

Navnath Barde 40

We are using Microsoft Graph API to read and update Outlook calendar events.

Normal (non all-day) events work correctly, but we consistently face issues with ALL-DAY events.

Scenario:

Organizer mailbox timezone: IST (UTC+05:30)
User creates:
1. Normal meeting: 10:00–10:30 IST
2. All-day event on 9 Feb
Events are fetched using: Prefer: outlook.timezone="UTC"

Graph API response:

Normal event (expected and correct):

start:
{
  "dateTime": "2026-02-09T04:30:00Z",
  "timeZone": "UTC"
}

All-day event:

{
  "isAllDay": true,
  "start": {
"dateTime": "2026-02-08T00:00:00Z",
"timeZone": "UTC"
  },
  "end": {
yaml
"dateTime": "2026-02-09T00:00:00Z",
"timeZone": "UTC"
  },
  "originalStartTimeZone": "UTC",
  "originalEndTimeZone": "UTC"
}

Problem:

For all-day events, Microsoft Graph always returns start/end as 00:00 UTC
Prefer: outlook.timezone header is ignored
originalStartTimeZone/originalEndTimeZone are also returned as "UTC"
Organizer timezone is NOT available in the event payload Because of this:
It is impossible to determine the actual local calendar day of the all-day event
Applications that store everything in UTC cannot correctly normalize all-day events
Date shifts occur unless custom logic is applied
The only workaround appears to be calling /users/{id}/mailboxSettings, which is user-dependent and requires additional permission

Questions:

Is this all-day event behavior by design in Microsoft Graph?
Is there any event-level or non user-dependent way to determine the organizer’s timezone?
Is /users/{id}/mailboxSettings the ONLY supported way to get organizer timezone?
Are there any official best practices from Microsoft for handling all-day events correctly without relying on user mailbox settings? We understand that all-day events are date-based, but without organizer timezone information in the event object, correct UTC normalization is unreliable.

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Answer 1

Kudos-Ng 13,275 Microsoft External Staff Moderator

Hi Navnath Barde,

Thank you for posting your question in the Microsoft Q&A forum.

At this time, I’m not aware of any official Microsoft documentation or confirmation that explicitly explains the behavior you have observed. However, similar behavior has been reported by multiple users in the past.

Recently, one user shared an alternative approach that may be helpful in your scenario. Specifically, it suggests determining the original time zone by inspecting the MAPI property returned via singleValueExtendedProperties.

You can refer to the original discussion and solution here: https://stackoverflow.com/questions/65349822/inconsistent-originalstarttimezone-for-all-day-events/79829561#79829561

Important: This link will take you to Stackoverflow, which is outside Microsoft’s domain. Please note that Microsoft is not responsible for the accuracy, security, or advertising on external sites.

I hope the information above helps clarify the situation you are currently encountering, and ideally provides you with another possible direction to further investigate or address the issue.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Kudos-Ng 13,275 Reputation points Microsoft External Staff Moderator

2026-02-05T13:06:24.32+00:00

Hi Navnath Barde,

Just checking in to see if you had a chance to review the previous response.

Your feedback would be very helpful in ensuring everything is on track.
Navnath Barde 40 Reputation points

2026-02-06T06:22:06.0066667+00:00

Thanks for the response.

We will try this approach and verify whether it works as expected on our side.

However, our main concern still remains regarding all-day events: how can we reliably determine the organizer’s/user’s timezone?

Is there any supported way to obtain the organizer timezone from the event itself, or any non user-dependent approach available?

Clarification on this would help us decide the correct implementation.
Kudos-Ng 13,275 Reputation points Microsoft External Staff Moderator

2026-02-06T07:28:18.0166667+00:00
Hi Navnath Barde,

Thanks a lot for following up.

I completely understand your concern about this behavior and how disruptive it can be. Let me clarify the key points:

Per the event resource documentation, there is no field that exposes the organizer’s time zone in the event itself. The organizer object only contains the organizer’s name and email address. As a result, you generally cannot determine the organizer’s time zone from the event payload. The supported way is to query GET /users/{id|userPrincipalName}/mailboxSettings, as you already noted.

The Mailbox Settings endpoint supports application permissions, so you do not need an interactive user sign‑in or delegated permissions for this call; you just need to grant the appropriate Graph application permissions and obtain admin consent. See the permissions section here: https://learn.microsoft.com/en-us/graph/api/user-get-mailboxsettings?view=graph-rest-1.0&tabs=http#permissions

As mentioned earlier, if you create the event via Graph, you can explicitly set the initial time zone so that you preserve the organizer’s intended zone from the outset. If your extended‑property workaround (reading the original time zone via singleValueExtendedProperties) proves reliable in your scenario, this may let you avoid calling GET /users/{id|userPrincipalName}/mailboxSettings for that particular use case.

I hope this helps.
Kudos-Ng 13,275 Reputation points Microsoft External Staff Moderator

2026-02-09T10:37:35.8366667+00:00

Hi Navnath Barde,

Just checking in to see if you had a chance to review the previous response.

Your feedback would be very helpful in ensuring everything is on track.

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Microsoft Graph all-day events return incorrect UTC start/end – organizer timezone not available

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