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A leap week calendar is a reformed calendar system in which each year consists of a whole number of weeks. Leap years have one week (or some other whole number of weeks) added, so each year begins on the same day of the week.

The ISO week is an example of such a calendar. It is a variation of the Gregorian calendar that is used (mainly) in government and business for fiscal years, as well as in timekeeping. In this system a year (ISO year) has 52 or 53 full weeks (364 or 371 days).

Leap week calendars vary on whether the concept of month is preserved and whether the month (if preserved) has a whole number of weeks.

Most leap week calendars take advantage of the fact that 400 Gregorian calendar years have exactly 20,871 weeks, so with non-leap years of 52 weeks, this means there are 71 leap weeks every 400 years. These include the Pax Calendar and CCC&T, as well as the ISO week dates.

One proposed calendar (The Bonavian Civil Calendar) has 159 leap weeks in a 896-year cycle, which has a mean year of 365.2421875 days. Josef Suran's World Calendar with Leap Weeks has a 62 year cycle with 11 leap weeks, which has a mean year of 365.241935 days.

Advantages of week calendars
Pro Con
  • There are no variations between day of week between years for a specific date.
  • The calendar starts on the same day and week every year.
  • Unlike the regular calendar, variations of years are limited to a possible addition of a leap week.
  • There are no fragments of weeks at the end of the year.
  • Unlike certain proposed calendar reforms such as the World Calendar and International Fixed Calendar, there is no need to modify the week.
  • A year with a leap week is at least 7 days longer than a year without a leap week, consequently the equinoxes and solstices must vary over 7 days, (i.e. ±3 of the average date), or even more, such as 19 days in the Pax Calendar.
  • The mere fact that the year may vary by seven days may be a stumbling block to adoption. Contracts, for example, set to expire within "five years" need to determine whether any leap years are included, making a year longer and perhaps changing the rent or mortgage or salary for that year.

Year Structures Edit

Calendars with leap week at the end
ISO week 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
Day
13 months 1 2 3 4 5 6 7 8 9 10 11 12 13 *
Bonavian 1 2 3 4 5 6 7 8 9 10 11 12 *
Sym454 1 2 3 4 5 6 7 8 9 10 11 12 *
30-31-30 1 2 3 4 5 6 7 8 9 10 11 12 *
Gregorian January February March April May June July August September October November December *
Quarter 1 2 3 4

Note that the new years of the calendars shown need not be synchonised.

External linksEdit

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