Subtracting two date columns in two different tables

[Ronning]

Hi, I have a problem with subtracting two date columns from different tables. 

I have tried this.       DATEDIFF(  SUM( 'Table' [Column] ) , SUM( 'Table' [Column]) , DAY ).

But when i drag this measuer into a table it gives me this message.

" An unvalid numerical representation of a datevalue has occoured"

Could this be because thera are some future date in one column that dosent exist in the other ? 

Thanks

[tamerj1]

Hi @Ronning 
If there is a relationship between th etwo tables then if table1 is at the many side and table2 is at the one side and assuming that 'Table1'[Column] is the earlier date and 'Table2'[Column] is the later date then you can use

# Days =
SUMX (
    'Table1',
    DATEDIFF ( 'Table1'[Column], RELATED ( 'Table2'[Column] ), DAY )
)

[Ronning · Accepted solution]

I found out the problem... It was just to change SUM to MAX.