This module allows you to calulate the day, week, period or quarter of a date
in a fiscal year, given a start date and either a target date or number of
periods and target date. This is often needed in business, where the fiscal
year begins and ends on different days than the calendar year. This module is
based on the Gregorian calendar. Using other DT calendar objects will return
results, but the behavior is unpredicatable for calendars that have more than
365 or 366 days.

WWW: http://datetime.perl.org/