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.
Middle-earth calendar is year 1421 on the Shire calendar. A year in the Shire is the same length as our year – 365 days, 5 hours, 48 minutes, 46 seconds. The Shire's calendar year is also divided into 12 months but all of 30 days. Five additional days are added to create a 365-day year. For the names of the months, Tolkien used reconstructed names derived from the Anglo-Saxons; in other words, they are Tolkien's take on what English would be actually using now if it had not adopted Latin names for the months (January, February, March, etc.). The "Yuledays" are the