It depends on exactly what you want to calculate. set up a new column and define it as a number (so use insert column, and choose "number1", "number2" or whichever one you prefer) then;
If its time remaining from todays date, use the formula

IIf(([Finish]-[Current Date])>0,([Finish]-[Current Date]),0)

the IIf statement means that you will get a 0 in the column if the task has no days left.

If you want it to show in whole days (depending on the way project is set up, it may well give a decimal because of the time being seen as a fraction of a day), try
CInt(IIf(([Finish]-[Current Date])>0,([Finish]-[Current Date]+1),0))

or CInt(IIf(([Finish]-[Current Date])>0,([Finish]-[Current Date]),0)) ; this will give number of days rounded down (first one) or rounded up(second).

If you want to show number of days from the status date, then use [Status Date] instead of [Current Date]

If none of these fit the bill, let us know and I can work some new ones