If you are looking to set it up so that it automatically fills in for whatever the current month is:
In A2:
=IF(COLUMN(A1)>DAY(DATE(YEAR(TODAY()),MONTH(TODAY())+1,0)),"",(TODAY()-DAY(TODAY()))+COLUMN(A1))
Copy across to AE2
or if you have the Analysis Toolpak installed:
=IF(COLUMN(A1)>DAY(EOMONTH(TODAY(),0)),"",EOMONTH(TODAY(),-1)+COLUMN(A1))
Format as date.