Wrong months in a year

hi guys,

i'm trying to get excel to work out the number of months within to dates:-

06/04/2010 to 05/04/2011
or
06/04/2011 to 05/04/2012
or
06/04/2012 to 05/04/2013

These are tax year dates and since the taxman regards it as a full year, i can only use these dates. The problem i have is that excel is classing these dates as 11 months, rather than 12 months just because of one day less...how can i correct this?

FYI, I'm currently using this formula:-

=DATEDIF(B3,C3,"m")


Thanks for your help