I know that.
According to your hint, i tried the following code
If Not IsNull([StartDate]) Then
If Not IsNull([EndDate]) Then
If (Format(StartDate, "YYMM") = Format(EndDate, "YYMM")) Then
Me.BillingMonth = Format(StartDate, "MMM-YY")
Else
Me.BillingMonth = Format(StartDate, "MMM-YY to ") &...