Take off weekends and leave only weekdays - SharePoint list column formula

Hello All,

I have two columns dates(Start Date and Submission Date) in a SharePoint List.

I create another column and called it Days Left. 

Days Left=Submission Date-Today's date

I created a formula which looks like this:

=((DATEDIF(TODAY(),[Submission Date],"D"))-INT(DATEDIF(TODAY(),[Submission Date],"D")/7)*2-IF((WEEKDAY([Submission Date])-WEEKDAY(TODAY()))<0,2,0)+1)

1-) The formula works but it does not give me the correct result.

2-) It gives this error (#NUM! )where there is no date or wrong date. How can I remove/hide this error.

Looking forward to hearing from you.

Thanks in advanced.