Canon:Common Year

In the World of Greyhawk campaign setting, the Common Year, or CY, is the basis of the common calendar. Years occurring before the Common Year are denoted with negative numbers, or are sometimes listed as "BCY" (Before Common Year).

There is no Common Year zero (0 CY), as the reckoning began with the first year, 1 CY, which must be accounted for when converting other systems of reckoning years prior to 1 CY, such as the Flan Tracking (FT, also known as the Flan Tally), Suloise Dating (SD, also known as the Suloise Dominion), Oeridian Record (OR, also known as the Oeridian Reckoning), Baklunish Hegira, (BH, also known as the Baklunish Hierarchy), or the Olven Calendar (OC),

Days, weeks and months within the Common Year are reckoned using the Greyhawk Calendar.

History
The Common Year Reckoning is an Oeridian, specifically an Aerdi, creation, and replaced the Oeridian Reckoning. The Common Year was established as the system of reckoning by Grand Prince Nasran I of the Great Kingdom of Aerdy in 645 OR (1 CY), when he declared universal peace throughout his the land, and took the title of Overking.