Get help with duplicate iCloud calendars

1. Open Calendar. If you don't see a list of your calendars, click the Calendars button in the upper-left corner.
2. Find the section labeled On My Mac. 
3. Compare the events in On My Mac to the events on your iCloud calendars. 
4. If your calendars in iCloud show all of your events and the calendars on your Mac show only duplicates, you can hide the calendars on your Mac. To hide a calendar, deselect its box in the section called On My Mac.

If you choose to delete calendars on your Mac, delete only those in the On My Mac section. Don't delete calendars in any other section, like iCloud, Subscriptions, Other, or other calendar services.

To delete calendars on your Mac, follow these steps: 

1. Make a copy of your iCloud calendar data.
2. In the On My Mac section, click the calendar that you want to delete. 
3. You can delete the calendar in two ways:
   • Choose Edit > Delete.
     
   • Right-click and select Delete.

Learn how to remove duplicate events in the Calendar app.

1. Open Outlook and click Calendar. If you can't see your list of calendars, expand the pane: Click the right arrow button above the Navigation Pane button (Outlook 2007), Folders button (Outlook 2010), or All Folders button (Outlook 2013 and later).
2. From the left viewing pane, find the section labeled My Calendars. In Microsoft Outlook, you can find your local calendars in My Calendars, also called Outlook DATA file. By default, this box should be checked so you have access to your local calendar.
3. Compare your events in My Calendars to the events on your iCloud calendars. 
4. If your calendars in iCloud show all of your events, and the calendars on your PC show only duplicates, hide the calendars on your PC. To hide a calendar, deselect the checkbox next to the calendar. If some events on your PC aren't in iCloud, try manually importing your events to iCloud. Open iCloud for Windows, deselect the “Mail, Contacts, Calendars, and Tasks” checkbox, and click Apply. Select the checkbox again and click Apply.

1. Make a copy of your iCloud calendar data.
2. In My Calendars on your PC, right-click the calendar that you'd like to delete and choose Delete Calendar. Outlook won't let you delete the default Calendar, but you should be able to remove other calendars that you have permission to delete.

1. Open Calendar.
2. Tap Calendars at the bottom of the screen.
3. Find the section Gmail.
4. Tap All Gmail to hide all of your Gmail calendars. Or tap a specific Gmail calendar to hide it.

Go to Settings > Calendar > Accounts, tap Gmail, then turn off Calendars.

To hide Holidays in the Calendar app on your iOS device:

1. Open the Calendars app.
2. Tap Calendars at the bottom of the screen.
3. Scroll down to the section labeled Other, and tap US Holidays or Birthdays to hide it.

To hide Holidays in the Calendar app on your Mac:

1. Open the Calendar app.
2. Go to the Calendar list on the left side of the window and find the section labeled Other.
3. Deselect US Holidays or Birthdays.

If you see multiple birthday events for a contact, check if you have more than one contact card for that specific person. Open the Contacts app, tap the Search field at the top, then enter the contact's name. If you see multiple results for the same contact, tap the contact, the tap edit to manage, delete, or consolidate their contact information.