365-day calendar 365-day calendar A 365-day calendar consists of exactly 365 days per year (no leap days), and is primarily used in computer models and as an assumption in every-day calculations. For example, a calculation of a daily rate may use an annual total divided by exactly 365. Interest rates in some banks are calculated using a 365-day calendar. Some Mesoamerican calendars used a 365-day year with no leap year, resulting in a gradual shift of the seasons relative to the calendar. This includes the Maya Haab' and the Aztec Xiuhpohualli calendars. Some versions of the Zoroastrian calendar also use a fixed
Adoption of the Gregorian calendar the Empire (except Scotland, which had already done so from 1600) changed the start of the civil year from 5 April to 1 January. Consequently, the custom of dual dating (giving a date in both old and new styles) can refer to the Julian/Gregorian calendar change, or to the start of year change, or to both. The British tax year traditionally began on Lady Day (25 March) on the Julian calendar and thus became 5 April, which was the "Old Style" equivalent. A 12th skipped Julian leap day in 1800 changed its start to 6 April. It was not changed