Aus der Designer Hilfe:
Dates can be compared and subtracted. Subtraction yields a numeric value representing seconds. To measure the difference between two dates in days, divide the result by 86,400, which is the number of seconds in a day. For example, if you have two date fields, date1 containing [07/01/01] and date2 containing [07/05/01], the following returns 345,600:
date2-date1
To display the result as 4 days instead of 345,600 seconds, use the following code:
(date2-date1)/86,400