Launch the Calendar app on your iPhone or iPad. Tap on the Calendars button in the bottom navigation. Tap on the Info button next to the calendar you’d like to share. Tap on the Add Person option under the Shared With section.
On your iPhone, go to Settings.
Select “Mail, Contacts, Calendars”.
Select your Google account (if you have it in your phone; if not, add it).
Go to “Calendars” and switch the toggle on.
This will sync all your calendars automatically. Done!
Can I sync my iPhone calendar to Google Calendar?