DateClass allows you to add a period to a date. You can also retrieve periods such as begin/end of month, begin/end of week, and begin/end of quarters.
DateSpanClass allows you to determine the span between two dates. The span can be a wide variety of different kinds of periods including year, month, week, weekdays, & quarters.
These classes are written by Steve Powell and can be downloaded from phpclasses.org oe from here (60 kb).
