The Barovian Calender was alternative calendar used by the people of the Zarovich Valley, beginning with the unification of Barovia from seperate city states by the von Zarovich family. Details about these events became scant after the rise of Strahd von Zarovich, when he forcibly took hold of the Zarovich Valley and abolished the Common Calendar. Any information after the Wedding That Never Was became especially sparse, as few records were kept in the terror of Strahd's dread domain.
Following the Common Calendar, Barovians used a lunisolar calendar that began on each month and year on the full moon. However, the calendar was only composed of twelve months, called "moons", composed of 28 days, or "darks". Rather than the month of Rebirth, every two to three years, a thirteenth month would occur known as the Hektavr or "Ghost Moon" would occur, where the Leylines between worlds became the thinnest.
The Ghost Moon could last longer than 28 days, seemingly occurring at the whim of Strahd. It was said that nightmarish creatures and strange visitors from other lands could easily pass through the valley during the Ghost Moon, and many thought it was the fault of the absence of Mother Night in the valley. Most Barovians were scared of the effects of the ghost moon and typically did not track these months when counting their age.