Mariam, this shouldn't be too tough.
You need to create a new calculated field for the previous year using the same formula as your current year, but with one additional test.
IF YEAR([Start Date])=YEAR([Start Date])-1 //this pulls in any records for the previous year
AND YEAR([Start Date])-1<=[parameter date]-1 //this does your comparison but based on the PREVIOUS year, not the CURRENT year
AND DATEDIFF('month',[start Date ],[parametre date ])= 0
I can't test this to be sure that it will work (it depends on a bunch of assumptions) but that's the general pattern you want to follow.