The Holidays calendar shows national holidays based on your computer’s region.
You can view a Birthdays calendar that automatically includes all birthdays listed in the Contacts app. If you set up a Facebook account in Calendar, you can also view a Birthdays calendar of your Facebook friends’ birthdays.
In Calendar, choose Calendar > Preferences, then click General.
Select “Show Holidays calendar.”
To change your region (to display different holidays), choose Apple menu > System Preferences, click Language & Region, then choose your region. In Calendar preferences, deselect “Show Holidays calendar” and select it again. For more information about changing your region, see Customize formats to display dates, times, and more.
In Calendar, choose Calendar > Preferences, then click General.
Select “Show Birthdays calendar.”
As you add or remove birthday information in Contacts, the Birthdays calendar in Calendar is updated. To change the Birthdays calendar, edit the information in Contacts.