The most-used Calendar of the PM world is the Imperial Solar Calendar, propagated by the Emperor Atsef IV the Scholar. It is used nowadays for secular purposes even among nations which historically had no love of the Empire of Atsef; the fact that its era begins in the year of the Prophet Ardamar's Solar Descent probably aided adoption among Monotheists generally. The calendar sees use even among non-Templars for secular purposes, especially trade.

The calendar has ten months, named for a series of divine names mentioned in the Book of the Lights. Intercalaries are considered formally apart from any month, but where a month name is required anyway, it is simply called "Intercalary." The word being obscure, it is sometimes treated as an eleventh, optional month by those unfamiliar with the calendar's origins.

The calendar has 372 days per year, 375 on leap years.

See also PM/Timekeeping, for the tracking of time within a single day.