A customizable theme calendar includes a set of date cells corresponding to an arbitrarily designated time period (e.g., a starting date and a target date), and a theme applied to the calendar. The theme corresponds to an event associated with the arbitrarily designated time period. The time periods and themes may correspond to recognized holidays such Halloween, Thanksgiving, Easter and so on, or to arbitrarily designated events having personal or familial significance, such as weddings, birthdays, anniversaries, etc. Such customized calendars may be designed and generated in connection with a computer system and calendar generation software.