The present invention provides a world timepiece including means (7, 13) for calculating a time inclusive of date information for a particular region, input means (8, 10) for designating a given initial time, means (7, 15) for calculating a given time based on the given initial time, and display means (6) operable to display either the time for the particular region or the given time. The timepiece further comprises means (14, 16, 17) for calculating an international date line time, comparison means (18) for comparing the international date line time with the time for the particular region and the given initial time respectively, and means (19) responsive to outputs from the comparison means for determining a date for the given initial time.