How can we calculate dates difference

ravi_ch -> You can also do using DAX.

Step 1: Create index column starting with 1 (Transform data -> Index column -> Start from 1)
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.

Hi ravi_ch ,

You can do this is Power Query. 

Step 1- Create an index column.
Step 2 - Add new custom column 

paste this code in it:
= try #"Added Index"{[Index]-1} [Date] otherwise null 

and then click on OK.
this step is going to take the date present in 2nd row to the first row.

 Step 3: Create another column which has your result

Result = DATEDIFF([date], [new column that we created], DAY)
ravi_ch -> If this works, the  please mark it as a solution.

ravi_ch 

you can create a measure

Measure = 
VAR _last=maxx(FILTER(ALL('Table'),'Table'[Date]<max('Table'[Date])),'Table'[Date])
return DATEDIFF(_last,max('Table'[Date]),DAY)

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.

but apply slicer like product mam it won't working.
like for each Product what is difference in days between each sale