I have a heading on a worksheet that shows the spread of work on that
sheet, which is always 13 months.

So the current heading reads

"Average Of data between Sept 2004 and Sept 2005"

I believe i can put this in the form of a formula where Sept 2005 will
always be the current month -1 and the Sept 2004 date will always be
the current month -14.

Does any one know the formula that would achieve this please.