It’s always a good idea to start by syncing your Mac’s iCal calendars with iCloud as that’s where you’re most likely to be storing the majority of your events and appointments. However, iCloud will merge every calendar of the same name that you link it with, so you’ve no need to worry about events cancelling each other out.
Head into System Preferences and find the iCloud preferences pane. If you haven’t used iCloud on your Mac before you’ll be asked to enter the Apple ID associated with it.
Once you’ve entered your ID you’ll be presented with a list of items to sync with iCloud. Click the checkbox located next to Calendars to start syncing iCloud with iCal.
iCloud displays a confirmation message to ask whether you’d like to merge the iCal information on your Mac with anything already on iCloud. Click Merge to begin this process.
Fire up iCal to see if the sync has worked. Click on the Calendars icon in the top-left corner. All of your calendars should now appear under the iCloud heading.
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