=1+(B1-A1)/365

If you want to account for leap years, use a third cell with 31-12-2008. If
this is in A2, use this formula:

=1+(B1-A1)/(A1-A2)

--
Kind regards,

Niek Otten
Microsoft MVP - Excel

"john" wrote in message
...
How do I calculate what percentage of a year has elapsed?
I have the date 31/12/09 in cell A1 and the date 31/05/09 in cell B1 and
then I do this: =B1/A1*100 but this formula is wrong.How should I do the
calculation?
Thanks, John