How to Calculate a Date in Excel

1. Populate today's date with the Today function. Type '=TODAY()' in a blank cell to return today's date. The Now function returns the date and the time stamp: '=NOW()'.
2. Calculate a future date by entering a date in a cell. Click on an empty cell and type '=cell reference number of days' where cell reference refers to the date that was entered and the number of days should be substituted for the actual number of days you want to calculate. For example, if we enter 5/22/2009 in cell A1 and want to know what the date will be in 21 days, the formula would be '=A1 21', which returns 6/12/2009.
3. Calculate a past date following the same procedure as in Step 2, but replace the plus sign with a minus. For example, if we enter 5/22/2009 in cell A1 and want to know what the date was 13 days ago, the formula would be '=A1-13', which returns 5/9/2009.
4. Calculate the number of days between two dates with the DAYS360 formula. Enter a start date and end date in two cells. Click on an empty cell and type '=DAYS360(start date,end date)', where the start and end dates would be substituted with cell references. In our example in Step 3, if we had the original date of 5/22/2009 in cell A1 and the calculated end date in B1, the formula would be =DAYS360(B1,A1), which returns 13 days.