0 (year) - Counting Intervals Without A Zero

Counting Intervals Without A Zero

The absence of a year 0 leads to some confusion concerning the boundaries of longer decimal intervals, such as decades and centuries. For example, the third millennium of the Gregorian calendar began on Monday, 1 January 2001, rather than the widely celebrated Saturday, 1 January 2000. Likewise, the 20th century began on 1 January 1901.

This rule arose because the Gregorian calendar begins with a year 1 instead of 0. Cardinal and ordinal numbering of years is therefore identical: The year 10 is the tenth year of the calendar and the end of the first decade. The year 11 is the first year of the second decade, and so on. In spite of this rule, years ending in 0, rather than 1, are commonly perceived as marking the beginning of a new decade, century, or millennium. Decades, however, are more used as a collective term (e.g. the 1930s) rather than a periodic term (e.g. 1930–1939).