I believe the syntax uses commas, rather than semicolons? try the following:
=DATEDIF(A1,A2,"MD")

HTH,
Keith

"MichDenis" wrote in message
...
Hi,

Does someone have an explanation ?

2 Dates in 2 cells
A1 = 01/31/2008
A2 = 03/01/2009

With this formula : =DATEDIF(A1;A2;"md")
The answer = -1

With this 2 dates :
A1 = 01/30/2008
A2 = 03/01/2009
With this formula : =DATEDIF(A1;A2;"md")
The answer = 0

Is it really a bug ?

Thank for your participation.