You cannot delete individual birthdays from the Birthday calendar. see "Remove the Holiday or Birthday calendar from Outlook.com or Office365" for more information.

Not surprisingly, there are more than a few users who don't Outlook to add birthdays to their calendar. Generally speaking, the best way to prevent this is by not putting birth dates and anniversaries in the contact fields. If you want to keep a record of important dates, add them to the notes field or use the User Fields.

However, if you want to use the birthday field, you can use a macro to remove the birthday event from the calendar. It's not 100% fool-proof and may not prevent every birthday from being added to the calendar, but it should delete most additions.

Remove Dates from Contacts

If you want to remove the dates quickly and (fairly) easily, use a group by view, grouping by the Birthday or Anniversary field then drag the contacts to the None field. You can hold Shift as you select as group of Contacts, which will speed the process up if you have a lot of contacts.

Remove Events from the Calendar

If the Contacts and Events are still linked, Outlook will delete the birthday or anniversary event when you remove the date from the Contact. However, its easy to break the link which will prevent Outlook from breaking the link. (Syncing with a device will often break the link).

Removing the dates from the calendar is simple: initiate a search for Birthday OR Anniversary and delete the items with those words in the subject. Hold Shift as you select the first and last items to delete a group of events at once.

Remove Dates from Contacts Tutorial

This video shows you how to use a group by view to remove dates from Contacts and use Instant Search to find Birthday and Anniversary events on your calendar.

In the Contacts folder:

1. Switch to a List view
2. Add the Birthday and Anniversary field to the view. In Outlook 2010, do this from View ribbon, View setting. In other versions, you can right click on the row of field names and choose Field Chooser. Birthday and Anniversary are under Personal Fields.
3. Right click on one of the new fields and choose Group by this field.
4. If another field is in the Group by box, drag it out.
5. Locate the Birthday: None group and drag the items to it. You can use Ctrl+A to select all or Ctrl+Click to select a group.
6. Repeat for the other field.

If the events are still linked to the Contact, Outlook will remove them from the calendar when you clear the contact.

To check, go the Calendar and type Birthday OR Anniversary in the Search field. Delete the events you don't want, using Ctrl+Click to select a group.

VBA to Remove Birthday Events

To use, copy then paste in the Outlook's VBA editor (press Alt+F11 to open it.) Click in the Start Up macro and press the Run button.

To test: go into the Calendar and search for Birthday. This will show all birthday events. Open a new contact form and size it so you can see the calendar screen. Create a contact with a birthday field and watch the calendar screen. If the macro is working, you should see it jump when you save and close the contact. If its not working, you'll see the new Birthday event.

Dim WithEvents mcolCalItems As Items

Private Sub Application_Startup()
    Dim objNS As NameSpace
    Set objNS = Application.GetNamespace("MAPI")
    Set mcolCalItems = objNS.GetDefaultFolder(olFolderCalendar).Items
    Set objNS = Nothing
End Sub

Private Sub mcolCalItems_ItemAdd(ByVal Item As Object)

    If Item.Class = olAppointment And _
       InStr(Item.Subject, "Birthday") Or InStr(Item.Subject, "Anniversary") > 0 Then
        With Item
            .Delete
        End With
    End If
End Sub