Additional Date Functions
Love Excel -- the one thing which is always a pain is working with dates (which is quite common). Although it is possible to do with long formulas these are really common things which I think deserve its own formulas:
1) Adding to dates with the type of component specified: e.g. it would be greate to add 1 month, or 2 years or 5 minutes to a date time in a very clear readable way: e.g. DATEADD(<component>,<date>,<increment>) ... to add 17 months to the date in A1: =DATEADD("M",A1,17)
2) Unhide DATEDIF ! It's there, but people don't know it.
3) A date "clamp" function. E.g. allowing the user to clamp to the first day of the month, the last day of the month, the first/last day of the quarter etc.
For compatibility reasons it would be great if these formulas can be saved in the workbook as an "expanded" formula e.g. the clamp formula might be saved as "=DATE(YEAR(A1), IF(MONTH(A1) <= 3, 3, IF(MONTH(A1)<=6, " to allow older versions to open and calculate it directly.