There is Birthday Calendar in Outlook and Outlook on the Web that just displays Birthday events. This is basically a filter of your overall calendar.
To display the Birthday calendar click on the Birthdays View in the Outlook or Outlook on the Web calendars:
Birthday events are attached to personal contacts and you cannot edit the Birthday calendar directly. To add a Birthday in Outlook, you must modify the personal contact and add a Birthday there. Then it will show up on your calendar and the Birthday calendar.
In Outlook on the Web you can add a birthday event which will also add a personal contact if one is not already there for that person.
On the Office 365 navigation bar, click the app launcher , and then click Calendar.
On the Calendar navigation bar, click New > Birthday event.
Under Details, enter the name, birth date, set a reminder, and click Save.
The birthday appears in your calendar.
Tips: Calendar is connected to your contact list in People, so: