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
Mesoamerican Long Count calendar The number of leap days, keeping in mind that the year 600 is not a leap year, is 10. Subtracting that from 317 remainder days is 307; in other words, the 307th day of the year 644 AD, which is November 3. To summarize: the Long Count date 9.10.11.17.0 corresponds to November 3, 644 AD, in the "Proleptic Gregorian calendar". To convert a Julian day to a Julian/Gregorian astronomical date (Proleptic Julian calendar before 46 BC): Use an astronomical algorithm such as the "Method of Meeus" to convert the Julian day to a Julian/Gregorian date with astronomical dating of negative