A leap week calendar is a reformed calendar system in which each year consists of a whole number of weeks. Leap years have one week (or some other whole number of weeks) added, so each year begins on the same day of the week. The ISO week is an example of such a calendar. It is a variation of the Gregorian calendar that is used (mainly) in government and business for fiscal years, as well as in timekeeping. In this system a year (ISO year) has 52 or 53 full weeks (364 or 371 days).