Two options (ther may be others).
1. Use another cell for the fixed date and refer to it =DATEDIF(B1,C1,"M")
2. Hard code the fixed date into the formula
=DATEDIF(B1,DATE(2006,12,8)=,"M")

The first option may be easier if you want to change the fixed date at any
time, but the second option is tidier as it doesn't need any extra cells in
the sheet.
--
Ian
--
"RC" wrote in message
...
I have a date difference formula =DATEDIF(B1,TODAY(),"M") which works
fine.
I thought I would amend the 'Today' bit of the formula to solve the
problem
where I want to know the number of months between a variable date and a
fixed
date.

e.g. variable date Fixed Date Months Difference
15/06/2006 31/04/2007 ?
22/09/2006 31/04/2007 ?
03/02/2006 31/04/2007 ?

Can you advise please.