Common Year (Greyhawk)

The Common Year (CY) Reckoning is a fictional dating system used in the World of Greyhawk campaign setting for the Dungeons & Dragons role-playing game.

In the mid-1970s, Gary Gygax created a campaign world called Greyhawk for the new fantasy roleplaying game called Dungeons and Dragons that he was helping to develop. In the 1980 TSR publication World of Greyhawk (TSR 9025), he included a brief timeline of twenty-one historical events that described a thousand years of history in order to explain how his world—the Flanaess—had arrived at its present state of affairs. There were five major cultures involved in this timeline, each of them with their own calendar system:

• Suloise: Suloise Dating or Suloise Dominion (SD)
• Olven: Olven Calendar (OC)
• Bakluni: Baklunish Hegira or Baklunish Hierarchy (BH)
• Flan: Flan Tally (FT)
• Oeridian: Oeridian Record or Oeridian Reckoning (OR)

One of the major events of Gygax's timeline was an invasion by the Oeridian people, which forced other cultures to the peripheries of this land and led to the formation of the Great Kingdom of Aerdy. The first emperor marked the start of this new empire with a new universal calendar, Common Year Reckoning.

Gygax calculated all events that had taken place before 1 CY as negative numbers, and since there was no 0 CY—the year previous to 1 CY was -1 CY—this forced an extra calculation when attempting to convert Common Year dates prior to 1 CY to the other calendar systems. However, by the start of Gygax's campaign (set as 576 CY), the Common Year Reckoning was used almost universally by most cultures, making conversions to the other calendar systems by dungeon masters largely unnecessary.

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