I seem to be getting differing results fromt he use of Yearfrac and edate
functions:

Example (all dates in mm/dd/yy format):

I have used the yearfrac function to calculate the difference in years
between two dates

Cell A4 contains First Date: 31/03/05
Cell D10 contains 2nd Date: 23/06/09

Cell C18 contains formula: Yearfrac(A4,D10,3) - Result is 4.23
I then want to add value in Cell C21 (1.5) to 4.23 and calculate the date:

=EDATE(A4,((C18+C21)*12))

Result is 30/11/2010

However, I also have a different cell containing the function:
=EDATE(D10,C21*12)

I get a different result: 23/12/2010

Can anybody tell me why the results are different or am I missing something
blindingly obvious?