|Introduction: The Time Period family deals with deterring the length of a time period. In Business Functions a timeperiod is specified by two variables Time and Base.|
Similar to the Date Difference family, you can either let DayCount and Periods default by just missing them out, or you can use the daycount options to accurately calculate the length of a timeperiod.
- TpY, TpM and TpD use the usual method of defining a timeperiod using Time and Base, where Time is the date at the start of the timeperiod and Base is either the length of the timeperiod, in months, or the date signifying the end of the timeperiod.
- A word or two about using Base to signify the end of the timeperiod: Business Functions" approach to start and end dates is to "include the first, exclude the last". This is consistent with what you do intuitively when to determine the number of days between, say the 3rd of the month and the 15th of the month to give 12 days. If you were including both dates the answer would be 13. This method also accords with what a day number in Excel really is - it"s a point in time representing the microscopic instant after midnight on that day - not noon or the end of the day. Finally it"s consistent with the way banks usually calculate interest. You will notice that in some of the more sophisticated projections functions in the library that involve a variable called ProjMode that you can, in these functions, optionally include both dates for the purposes of accruing something.
- There is also in this family a very useful function that just determines if an event occurs in a particular time period, called Occurs, that is often used within some of the other Business Functions.