Step-by-Step...

Create Birthday Reminders Using Contacts.app

Often people add birthdays directly onto their calendar, forcing a repeating annual reminder... Yet Apple makes keeping track of birthdays easier by adding a birthday reminder within 'Contacts'...

Click on 'Calendar' in the dock...

Go to 'Contacts.app' on the dock

Either add a new Contact... Click and hold the plus icon '+'...  select 'New Contact'...  

-OR- Search for, then select an existing 'Contact' > click 'Edit' button...  type the 'Birthday'...

 the date, and include the year, if you prefer the Contact's age to show on Your Birthday's Calendar.  >  Click 'Done'...

The Apple Calendar will present the birthday reminder.

Do you prefer more than 1 day warning, before all Birthday ALERTS? Upper-left corner > click Calendar menu > Preferences > Alerts  > click the pop-up...

Click off the Calendar...  

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