Outlook is not syncing birthdays correctly.

Question

My calendar often shows clients birthday one day early

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Answer 1

Hi Paul Beauchamp,

Thank you for reaching out to Microsoft Q&A forum.

The behavior where Birthdays on Outlook.com appear one day early is usually related to how all‑day events are interpreted across different time zones. Please follow the steps below to correct the display:

1. Verify and correct your time‑zone settings on Outlook.com

• Go to Settings > Calendar > View > Time zones, select the correct Display my calendar in time zone, and save the change.

Reference: Manage time zone settings in Outlook

2. Refresh (rebuild) the “Birthdays calendar”

• Navigate to Calendar > Add calendar > Birthdays, switch Turn on the birthday calendar to Off, wait 1–2 minutes, then turn it on again.

Please note: It may take several hours for all birthdays from your contacts to fully appear after the calendar is rebuilt.

3. Correct any remaining birthdays that still show the wrong date

• Open People (Contacts) > choose the contact > re‑enter the Birthday field > Save.
• This prompts Outlook to recreate the birthday entry with the correct date.

Please feel free to let me know if you have any further updates, thanks.

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Answer 2

my outlook calandar birthdays are not syncing to my contacts

Answer 3

The issue is a known problem with birthdays syncing one day off between Outlook and mobile devices when using Exchange Server 2016 or 2019, especially in certain time zones (for example, CET).

To correct new and future birthday syncs:

1. On the Exchange server, install the required cumulative update:
   • For Exchange Server 2019: install Cumulative Update 5 or a later cumulative update.
   • For Exchange Server 2016: install Cumulative Update 16 or a later cumulative update.
2. After the update, newly created or updated contacts with birthdays will sync with the correct date to devices such as the iOS native mail app.

For birthdays that are already wrong on calendars:

1. Edit and save the contact’s birthday again in Outlook. This forces a fresh update so the corrected date syncs properly.
2. If there are many incorrect birthdays, clear the birthday calendar on the device or in Outlook and then re-add the birthdays so they are recreated with the correct dates.

Note that it is technically not possible to retroactively fix already-created birthday entries purely by installing the update; existing entries must be updated or recreated using one of the workarounds above.

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References:

• Birthday isn't correctly synced to iOS native mail app in Exchange Server 2019 and 2016
• February 10, 2015 update for Outlook 2013 (KB2956087)