How can we calculate dates difference

Hi ravi_ch , Please try this:
Step 1: create index column using dax:
Index_column = RANKX(ALL('Tablename'),[Date])

Step 2: using DAX create a new column

PreviousRow = Lookupvalue(tablename[Date], tablename[index_column], tablename[index_column] -1)
Step 3: Create another column for counting the difference

Count = DATEDIFF([Date], [PreviousRow], DAY)

ravi_ch  -> Mark this as a solution & hit the thumbs up, if it works for you. Thanks.