A small project plan with start, due and done dates. Each task asks for one column of answers from row 2 down to row 7 (write the formula in row 2 and fill it down), or a single cell.
Choose between plain subtraction (calendar days), NETWORKDAYS and WORKDAY (working days), EDATE and EOMONTH (whole months), WEEKDAY and TEXT (days of the week). Empty Done cells mean the task isn't finished.