The Gregorian calendar is the system most people use today to keep track of time. It was created long ago to fix problems with older calendars that didn’t match up with the seasons. This calendar has 12 months, with a total of 365 days in a year—except every four years when we add an extra day (called a leap year) to keep things in sync with the sun.

In a fantasy TTRPG setting, you can think of the Gregorian calendar as a “common” calendar used by most kingdoms and empires to track time, plan harvests, or schedule festivals. Each month could be tied to a god, a season, or a celestial event, and leap years might hold magical significance, rare celebrations, or even strange omens.