The dates should be in Date format.
While you can define a calculation field to extract the number or name of the month of a date field, either option doesn't sort easily in the desired order in all cases.
Instead, I define a calculation that I learned from Comment here in this Forum:
DateField - Day ( DateField ) + 1
This calculation returns a date that is the first day of the month for all dates of that month. Since this is a date field I can sort by this field and the records will be grouped correctly by month in the same order as the months are listed in the calendar and will even sort correctly if I have records from more than one year.
When you place this calculation field on your layout, you can format it in the inspector to just display the name of the month.
Create two fields
DateStartMonthNumber = Month ( DateStart )
DateStartMointhName= MonthName ( DateStart )
Create a sub-summary break based on DateStartMonthNumber, sort by DateStartMonthNumber, but put the DateStartMonthName field in the sub-summary section.
I remember that calc from Comment - very good!
Ok Phil, Im a little confused so if my date field is "start date" them caluclation for my new field will be
start date - Day ( start date ) + 1
is that right?
Yes, and if start date is January, 3, 2011, this calculation returns January 1, 2011. If you enter any other January 2011 date you get the same date, 1/1/2011.
Make sure that this calcualtion is set to return "Date" as it's data type.