You can export your calendars and save the file in the ICalendar .ics format. iCalendars are the standard for calendar data exchange over the Internet, and .ics is the standard format for iCalendar information.
Export is available from your Options>Import/Export tab.
To export an iCal calendar:
In the Options tab, click the Import / Export tab.
In the Export section, select the type as Calendar and in the File field, browse to the calendar folder to export.
Select where to save the .ics file and click OK.