How to export one calendar and import it into another in macOS Sierra

In macOS Sierra’s Calendar app, you can move all events from one calendar to another by exporting one calendar and importing it into another.

If you use iCloud calendars or a calendar server account, you don’t need to export and import calendars to back them up. Your devices’ calendars are synced; when you set up new devices to use the account, your calendars are restored from the cloud or from the calendar server and you don’t need to restore from a backup.

To merge an entire calendar with another, export the calendar, import it into a calendar, and delete the old calendar.

To export a calendar’s events:

  • Click the calendar’s name in the calendar list. If you don’t see the calendar list on the left, choose View > Show Calendar List.
  • Choose File > Export > Export.
  • Choose a location, then click Export. The events are exported to an calendar (.ics) file.

To export all calendars:

  • Choose File > Export > Calendar Archive.
  • Choose a location, then click Save.

To import events into a calendar:

  • If you want, create a new calendar for the events.
  • Choose File > Import.
  • Select the file with the events, then click Import.
  • Choose the calendar to add the events to.
  • You can also drag a file with events to Calendar. The events are added to the calendar selected in the calendar list.

To import calendars from an archive file: 

  • Choose File > Import.
  • Select the archive file, then click Import.

Note that importing an archive file replaces all of your current calendar information.

(This how-to is based on my experiences and info on Apple's support pages — where the images come from.)