Abstract: A perpetual calendar that simultaneously and individually displays all twelve months of any predetermined year. The perpetual calendar includes an outer housing sleeve having twelve month-windows, a middle panel movably disposed inside the sleeve, and a numerical calendar grid adorning the middle panel behind the month-windows. The preferred embodiment of the perpetual calendar also includes positioning structure for orienting the middle panel and therefore the calendar grid among fourteen possible yearly positions, as well as indicia for displaying the current yearly position in which the calendar is oriented. The calendar grid includes twelve month-grids that are each configured to display only a single particular month of the year and to display the precise number of days in that particular month. Each of the month-grids includes a common year grid movable among seven common year positions and an adjacent leap year grid movable among seven leap year positions.