Let's see how to get the number of days in the month. You may need it to the reports or dashboards which you will create in the spreadsheet. There are several ways to create such a formula.
The first formula is:
=DAY(DATE(YEAR(NOW()),MONTH(NOW()) + 1,0))
The other way I know is:
Please note that this formula will only for Excel 2007 onwards. For Excel 2003 you can use only the first formula (or move to the newer version of Excel :-)).