Out of the Abyss
Calendar of Harptos
There are 365 days in the year, split up into twelve months of thirty days each with five holidays that fall between some months. The names of the months are given in both the formal names and the common ones. Each week consists of ten days, called a tenday.
The holidays are Midwinter, Greengrass, Midsummer, Highharvestide and The Feast of the Moon. Midwinter falls between Hammer and Alturiak, Greengrass between Tarsakh and Mirtul, Midsummer is between Flamerule and Eleasis, Highharvestide is between Elient and Marpenoth, and The Feast of the Moon is between Uktar and Nightal.
The holidays do not fall on the actual day the season changes. The 19th of Ches is the Spring Equinox, the 20th of Kythorn is the Summer Solstice, the 21st of Elient is the Autumn Equinox and the 20th of Nightal is the Winter Solstice.
Every four years, another holiday called Shieldmeet is added as a leap day immediately following the Midsummer holiday.