If you don't use a particular calendar or just want to declutter your calendar list, it's easy to delete calendars on an iPhone. You can remove iCloud calendars as well as Google, Yahoo, and any other calendars you may have added to your phone.
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Delete an iCloud Calendar on your iPhone
If you want to remove an iCloud calendar, you can use your iPhone's Calendar app itself to do so.
To get started, launch the Calendar app on your iPhone. At the bottom of the app, tap “Calendars.”.
On the “Calendars” screen, next to the calendar you want to delete, tap the “i” option.
You will land on an “Edit Calendar” page. Here, at the bottom, tap “Delete Calendar.”
And your selected calendar has now been removed from your iPhone.
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Remove a Google, Yahoo, or other calendar from your iPhone
If you've added an external calendar from your other online accounts to your iPhone, use the Settings app to delete those calendars. Note that this process only removes your calendars from your iPhone; those calendars still exist in your actual online account.
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To get started, open the Settings app on your iPhone and tap “Passwords & Accounts.”.
On the “Passwords & Accounts” page, select the account you want to delete a calendar from. This can be your Gmail, Yahoo, or any other account.
On your account screen, turn off the “Calendars” option. This stops calendars from syncing from that particular account to your iPhone.
You'll see a menu open from the bottom of your phone's screen. To remove all your calendars from the selected account on your iPhone, tap "Delete From My iPhone" in the menu.
And you have successfully gotten rid of unwanted calendars and their events from your iOS device.
Information source: howtogeek.com
