On the navigation bar, select Calendar.
From your Calendar list, select the other calendar(s) you want to view in addition to the default calendar.
To view the calendar side-by-side, in the Arrange group, select Split view.
To view multiple calendars in a single calendar view, in the Arrange group, deselect Split view. The calendar events appear overlayed on the default calendar with their assigned color.
View multiple calendars in Outlook for Mac