1] Add days directly If the expiry period is defined in days, you can calculate the expiry date by simply adding the number of days to the starting date using the + operator.

You should have experience with Excel before trying to use formulas to calculate what day of the week the 15th of a given month is, and you have several options to do this.

If you need to count or calculate number of Leap Years between two dates in Excel or list of two dates in Excel, make use of this formula to get things done.