Hi Bernie, effem,

With your start date in A1, and your end date in B1, the formula

=((YEAR(B1)-YEAR(A1))*12+MONTH(B1)-MONTH(A1)-1+(DATE(YEAR(A1),MONTH(A1)+1,0)
-A1)/DAY(DATE(YEAR(A1),MONTH(A1)+1,0))+(DAY(B1))/DAY(DATE(YEAR(B1),MONTH(B1)
+1,0)))*1000


Also
=(DATEDIF(A1,B1,"m")-DAY(A1)/(32-DAY(A1-DAY(A1)+32))+DAY(B1)/(32-DAY(B1-DAY(B1)+
32)))*1000

Regards,

Daniel M.