How can we calculate dates difference

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.