I was recently working on a project where we wanted to display a SharePoint list or calendar by grouping items by month. This is not a SharePoint default but can easily be accomplished by creating a new field.
Simply create a new field that is is a “Calculated column (calculation based on other columns)” and use the formulas below. Note that the formulas are creating the field based on the “Start Time” value. This can be customized as needed.
Month Formula (Year/Month, example “2015/08”)
=IF( [Start Time]="", "No start time", YEAR([Start Time])&"/"&RIGHT("0"&MONTH([Start Time]),2))
Year Formula (Year, example “2015”)
=IF( [Start Time]="", "No start tiime", ""&YEAR([Start Time]) )