HELP!! DAX : Date Diff

Newbie12345 

Use this measure as a calculated column in your table and make sure to change the table name as per yours:

Date Diff = 
VAR __MaxDate = 
    CALCULATE(
        MAX( Table03[Date] ) , 
        ALLEXCEPT(Table03 , Table03[ID] , Table03[Category] )
    )
VAR __PrevDate = 
    CALCULATE(
        MAX( Table03[Date] ) , 
        Table03[Date] < __MaxDate,
        ALLEXCEPT(Table03 , Table03[ID] , Table03[Category] )
    )
RETURN
    IF( Table03[Date] =  __MaxDate && __PrevDate <> BLANK() ,INT (__MaxDate - __PrevDate ) ) 

Hi, Newbie12345 

make a new column using below code

Column = 
var a = 'Table'[date]
var b = 'Table'[id]
var c= 'Table'[category]
var d = MAXX(FILTER('Table','Table'[date]<a && 'Table'[category]=c && 'Table'[id]=b),'Table'[date]) 
var e=  IF(d=BLANK(),'Table'[date],d)
var f= CONVERT('Table'[date]-e,INTEGER)
return
f

just adjust table and column name