How to calculate the 'number of DAYS TO GO'?

If I am at Sunday and have to countdown till Friday, do I count Sunday in my countdown, which makes 'Days to go' = 5, or since Sunday is going on, I DONOT count sunday and 'Days to go' becomes 4. Oh and do I count Friday as Day '0'?? (donot calculate in hours here..its 'DAYS TO GO')