Calculating Month difference between Dates

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Hi,

I have Data looks like bellow .

Emp No.   Occurrence   Partnership Level   Partnership Level Date   Months Difference 

1                1                   Level1                     1/1/2006                         Months (12/1/2007-1/1/2006)

1                 2                  Level2                      12/1/2007                      Months ( 3/2/2009 - 12/1/2007)

1                 3                  Level3                       3/2/2009

I wan another column in the report Months Difference which will be Difference from next Partnership Level Date to Current. Ex. for 1st occurrence it will be (12/1/2007 - 1/1/2006), for 2nd it will be ( 3/2/2009 - 12/1/2007)

Can you please help.

Thanks,

Vijay