The procedure to merge multiple Outlook Calendars is really quite simple and can be done in one minute or less by following these three steps:
Step 1: Click on the Calendar Tab in the Outlook Navigation Pane.
Step 2: Select the Outlook Calendars you wish to merge.
Step 3: Right-click on the Calendar Tab you wish to merge and select the Overlay function. This step can be repeated to merge multiple Outlook Calendars.
Note: To undo the merge, click on the Calendar Tab and select the Overlay function again.