A timepiece calendar system (100) including:—a date mobile (1);—a first device (3) for indexing the position of the date mobile;—a second device (4) for indexing the position of the date mobile;—an element (70, 3b, 4b, 40) for activating and deactivating at least one of the first and second indexing devices, the indexing of the date mobile by one or the other of the first and second indexing devices being mutually exclusive.