The ISO week date system is a leap week calendar system that is part of the ISO 8601 date and time standard. The system is used (mainly) in government and business for fiscal years, as well as in timekeeping.
The system uses the same cycle of 7 weekdays as the Gregorian calendar. Weeks start with Monday. ISO week-numbering years have a year numbering which is approximately the same as the Gregorian years, but not exactly (see below). An ISO week-numbering year has 52 or 53 full weeks (364 or 371 days). The extra week is here called a leap week (ISO 8601 does not use the term).
A date is specified by the ISO week-numbering year in the format YYYY, a week number in the format ww prefixed by the letter W, and the weekday number, a digit d from 1 through 7, beginning with Monday and ending with Sunday. For example, 2006-W52-7 (or in compact form 2006W527) is the Sunday of the 52nd week of 2006. In the Gregorian system this day is called 31 December 2006.
The system has a 400-year cycle of 146097 days (20871 weeks), with an average year length of exactly 365.2425 days, just like the Gregorian calendar. In every 400 years there are 71 years with 53 weeks.
The first week of a year is the week that contains the first Thursday of the year. It is also (equivalently) the week containing the 4th day of January.
| December 2012 | |||||||
| Wk | Mo | Tu | We | Th | Fr | Sa | Su |
| (48) | 26 | 27 | 28 | 29 | 30 | 1 | 2 |
| (49) | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| (50) | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
| (51) | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| (52) | 24 | 25 | 26 | 27 | 28 | 29 | 30 |
| (1) | 31 | 1 | 2 | 3 | 4 | 5 | 6 |
Read more about ISO Week Date: Relation With The Gregorian Calendar, Advantages, Disadvantages, Other Week Numbering Systems
Famous quotes containing the words week and/or date:
“Jesus would recommend you to pass the first day of the week rather otherwise than you pass it now, and to seek some other mode of bettering the morals of the community than by constraining each other to look grave on a Sunday, and to consider yourselves more virtuous in proportion to the idleness in which you pass one day in seven.”
—Frances Wright (1795–1852)
“Yesterday, December 7, 1941Ma date that will live in infamy—the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan.”
—Franklin D. Roosevelt (1882–1945)