Implementing Today function and Outstanding days

To use Today function in your SharePoint calculated column, you need to create a dummy column named as "Today" and then you can create a calculated column named as "Current Date". In the custom formula section of "Current Date" write =Today and save.Then Delete the Today column that you had created first. Your Current Column will now show you the Current Date system date.

If you are calculating the outstanding Days for an item since it is Date Opened then you can create custom column and write a formula for that like below:

=DATEDIF([Date Opened],IF(NOT(ISBLANK([Date Closed])),[Date Closed],[ Current Date]),"D")

This formula will calculate the No. of days for an item since Date Opened.