iOS Calendar SyncSo, you have several different Google Calendars, but have only managed to sync the primary one with your iPhone and iPad. Not to worry. Though it’s not the most intuitive system, by following these instructions you’ll be up and running in no time.
Here’s how to get all of your Google calendars working on your iPhone  or iPad:
  1. First, lets make sure your Calendar is properly synced, and the process is the same on both devices.
  2. Go to Settings, then open Mail/Contacts/Calendars.
  3. Next, select Add Account and Gmail.
  4. If however, you have already added your Gmail account, then instead of Add Account, choose Gmail from the account list. From here, toggle the Calendar switch to On.
  5. Otherwise, add your Google account information and a description of the calendar, and ensure that the Calendar option is switched on. Syncing will begin when you next open the Calendar app on your iPhone or iPad.
Next you must choose which calendars to sync:
  1. To do this, you need to visit the following Google
  2. Provided you’re signed into your Google account, on this page you’ll see a list of all your calendars, with a check box against them.
  3. Tick the boxes of the calendars you want to sync with the iPhone and iPad, then click save.
Once again, open the Calendars app and wait for it to sync. That’s it, all your calendars should be ready and waiting for you.