Calendar world for civil purposes. It is a purely solar calendar, with a cycle of leap days in a 400-year cycle designed to keep the duration of the year aligned with the solar year. Each Gregorian year has either 365 or 366 days (the leap day being inserted as 29 February), amounting to an average Gregorian year of 365.2425 days (compared to a solar year of 365.2422 days). It was introduced in 1582 as a refinement to the Julian calendar which had been in use throughout the European Middle Ages, amounting to a 0.002% correction in the length of the year.
Mesoamerican Long Count calendar 206, which corresponds to the year 600 AD. Next, divide this number by 365 days (vague year). The remainder is 44.86849 years, which is 44 years and 317 days. The full year date is 644 AD. Now calculate the month and day number, taking into account leap days over the 44 years. In the Gregorian Calendar, every fourth year is a leap year with the exception of centuries not evenly divisible by 400 (e.g. 100, 200, 300). When the year is divisible by 400 (e.g. 400, 800, etc.), do not add an extra day. Our calculated year is 644 AD.