From Wikipedia, the free encyclopedia.
The 53-week calendar is a variaton of the Gregorian calendar that is used (mainly) in business for fiscal years, as well as in timekeeping. In this calendar, the year does not necessarily end on a specific day (e.g., January 31 or December 31). The year does, however, end on a day of the week (e.g., the last Friday in December). Therefore, weeks and months of equal length are allowed to exist. Some years can only be 52 (full weeks), while others can be 53 weeks (371 days).
The ISO week is an example of such a calendar.
