Different companies use different fiscal years and different fiscal periods within those years. Most fiscal years are based on the familiar Gregorian calendar having twelve months from January to December, with 28 to 31 days per month. However, fiscal years usually begin on a day other than January 1. For example, 's fiscal years run from November 1 to October 31. Moreover, fiscal years can begin on a day other than the first day of one of the months.
Some companies use standard retail calendars, which still have twelve periods per year, but usually a total of 52 weeks (364 days) in four 13-week quarters. Other companies use non-standard retail calendars, which can have more than or fewer than twelve periods per year, and where the periods, quarters, half-years, and years can all vary in length. For information about standard and non-standard retail calendars, see Generating Periods for Retail Calendars.