Humans on the continent of Addar tend to use either the Ovidoric or Imperial calendars to mark the passage of days.
Ovidoric calendar
The Ovidoric calendar, also called the Calendar of Ovidor or the Common Calendar, is a system of organizing the 366 days of the Eamon year into weeks and months. It's the calendar followed by the people of the Kingdom of Evenhold and most surrounding lands, and is usually paired with the dating system known as the Years of Anharos.
Named for the astronomer and astrologer Ovidor who is said to have devised it, it arose after the downfall of the Old Empires as a simpler alternative to the Imperial calendar and was already widely used by the human nations of the Malphigian Basin when the kingdom of Aevinn was established in 515 BA.
The calendar year begins on the winter solstice (in the northern hemisphere) and is divided into 61 weeks, each consisting of six days. The calendar also breaks the year into eight months, each of which consists of 46 days, except for the first and last which have 45.
45 + 46 + 46 + 46 + 46 + 46 + 46 + 45 = 366
On leap years, which occur only every 239 years, the final month gains an extra day.
The even divisibility of most years into exactly 61 weeks means that the starting weekday of each month remains unchanged for centuries, making physical calendars highly reusable.
Imperial calendar
This calendar, widely used in the Old Empires of Addar, is known by various names today but is most often called the Imperial calendar, or sometimes just the "old calendar". It divides the 366 days of Eamon's year into two blocks of seven months (the Young Seven and the Old Seven), each consisting of 26 days, with a single intercalary day placed between each block that's part of no month (the Day of Suns and the Day of Moons):
26 + 26 + 26 + 26 + 26 + 26 + 26
+ 1
+ 26 + 26 + 26 + 26 + 26 + 26 + 26
+ 1
= 366
Leap-days, occurring only every 239 years, are treated as a third intercalary day (the Day of Souls) added to the end of the year.
Though replaced by the newer Ovidoric calendar in much of central Addar, versions of the Imperial calendar (that keep the 26×7×2+2 arrangement) are still in use in the Northern Reaches, in eastern lands like Knieriem, and in some other corners of the continent, though with varying systems of year-numbering.
Years of Anharos
The Years of Anharos (originally Years of the Sun) is a dating system followed in the Kingdom of Evenhold and much of middle Addar that begins shortly after the victory of King Anharos and the Alaxaran gods over the Great Old Ones in the Great Battle of Darkness 1,200 years ago. Years since that point are identified as YA, while years before it are identified as BA (before Anharos). For example, Anharos lived from 36 BA to 49 YA.
Anharos decreed the start of the new reckoning as one of his earliest official acts as the first king of the united Kingdom of Evenhold, naming it the "Years of the Sun" in honor of the sun-god Alaxar. However, following the death of Anharos in 49 YA it became more commonly identified with the name of the beloved king.
The dating system reset the year but otherwise kept the same 6-days-per-week, 61-weeks-per-year arrangement (the Ovidoric calendar) already in use in Aevinn.
Other uses
"The Years of Anharos" may also refer to the historical period from 1 YA to 201 YA when the House of Anharos — the king or his lineal descendants — ruled the Kingdom of Evenhold. The period ended with the War of the Twins and the rise of the Council of Twelve.
