CalenGoo can sync itself with your Google Calendar and with your iPhone/iPod/iPad’s calendar. But it cannot sync between both, it can only sync itself with both and aggregate their events and calendars in its views.
However it contains at least one solution for this problem, it contains a function to copy the content of a calendar of the iPhone/iPod/iPad’s calendar app into a calendar of your Google Calendar account. This can be useful if you have existing data on your iPhone/iPod/iPad but would like to start using Google Calendar instead. Then you can copy your existing data this way and afterward disable “Show iPhone/iPod/iPad calendars” to work only with Google Calendar.
You can find this function under “Settings > Data Migration”. It is only visible if “Settings > Accounts > Show iPhone/iPod/iPad calendars” is turned on. There you can choose a source calendar, a time range and a destination calendar. It is recommended to use an empty destination calendar (please see here how to create additional calendars: Calendars). This way you can simply delete and re-create it if something goes wrong. You can create such an empty calendar by clicking “Create new calendar” under “My calendars” on the left of the Google Calendar website.
This “Data Migration” function will not check for existing events in the destination calendar. So if you run it twice, you will have all events twice in the destination calendar. That’s another reason why it is a good idea to use an empty destination calendar.
You can watch a video how the whole copy process should look like, just click the image below or download it from http://www.calengoo.com/DataMigration.mov.
Using the "Data Migration" function you can copy your existing events from the iOS calendar into Google Calendar. This works fine if you don’t need the iOS calendar afterward any more and use Google Calendar instead. However in some cases this isn’t possible, e.g. if your iOS calendar contains a calendar that is synced with an Exchange server and thus it isn’t sufficient to sync it only once. If you are looking for a way to automatically sync such calendars at a regular interval with Google Calendar (instead of only once), please take a look at the app SyncCal.