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Birthday Events Showing Twice

Sources

In general, birthdays can originate from these sources:

  1. Manually entered in your calendar
  2. From your iOS device contacts (visible in a separate equally named category at the bottom of all your calendars).
    bday2a.png
    Facebook will enrich your contacts with birthdays too.

Duplicates

Duplicate birthdays can be caused by:

  1. A duplicate contact, resulting in a birthday for both
  2. iCloud duplicating your birthdays.

To reset your sync:

  1. Go to device Settings
  2. Go to Passwords & Accounts (or Accounts & Passwords in iOS11, Contacts in iOS10 or Mail, Contacts, Calendars in iOS9 and below)
  3. In the Accounts section select the one containing your Contacts (normally iCloud one)
  4. Turn OFF Contacts
  5. Reboot your device
  6. Turn ON Contact again