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Information about Iso Week Date

Calendars
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Common use Chinese Islamic Gregorian ISO Astro Julian
Calendar Types
Lunisolar Solar Lunar
Selected usage Armenian Bah' Bengali Berber Buddhist Coptic Ethiopian Germanic Hebrew Hindu Indian Iranian Irish Japanese Javanese Malayalam Maya Nanakshahi Nepali Nepal Sambat Tamil Thai: Lunar – Solar Tibetan Vietnamese Zoroastrian
Calendar Types
Original Julian Runic
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 years have a year numbering which is approximately the same as the Gregorian years, but not exactly (see below). An ISO year has 52 or 53 full weeks (364 or 371 days). The extra week is called a leap week, a year with such a week a leap year.

A date is specified by the ISO 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 its most compact form 06W527) 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 146,097 days (20,871 weeks), with an average year length of exactly 365.2425 days, just like the Gregorian calendar. Since non-leap years have 52 weeks, in every 400 years there are 71 leap years.

Relation with the Gregorian calendar

The ISO year number deviates from the number of the Gregorian year on, if applicable, a Friday, Saturday, and Sunday, or a Saturday and Sunday, or just a Sunday, at the start of the Gregorian year (which are at the end of the previous ISO year) and a Monday, Tuesday and Wednesday, or a Monday and Tuesday, or just a Monday, at the end of the Gregorian year (which are in week 01 of the next ISO year). In the period 4 January–28 December and on all Thursdays the ISO year number is always equal to the Gregorian year number.

Mutually equivalent definitions for week 01 are:
  • the week with the year's first Thursday in it
  • the week with the year's first working day in it (if Saturdays, Sundays, and 1 January are not working days)
  • the week with January 4 in it
  • the first week with the majority (four or more) of its days in the starting year
  • the week starting with the Monday in the period 29 December - 4 January
  • the week with the Thursday in the period 1 - 7 January
  • If 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01. If 1 January is on a Friday, Saturday or Sunday, it is in week 52 or 53 of the previous year.
Note that while most definitions are symmetric with respect to time reversal, one definition in terms of working days happens to be equivalent.

The last week of the ISO year is the week before week 01; in accordance with the symmetry of the definition, equivalent definitions are:
  • the week with the year's last Thursday in it
  • the week with December 28 in it
  • the last week with the majority (four or more) of its days in the ending year
  • the week starting with the Monday in the period 22 - 28 December
  • the week with the Thursday in the period 25 - 31 December
  • the week ending with the Sunday in the period 28 December - 3 January
  • If 31 December is on a Monday, Tuesday, or Wednesday, it is in week 01, otherwise in week 52 or 53.
The following years have 53 weeks:
  • years starting with Thursday
  • leap years starting with Wednesday

Examples

  • 2005-01-01 is 2005-W00-
  • 2005-01-02 is 2005-W00-
  • 2005-12-31 is 2005-W00-
  • 2007-01-01 is 2007-W00- (both years 2007 start with the same day)
  • 2007-12-30 is 2007-W00-
  • 2007-12-31 is 2007-W00-
  • 2008-01-01 is 2008-W00- (Gregorian year 2008 is a leap year, ISO year 2008 is 2 days shorter: 1 day longer at the start, 3 days shorter at the end)
  • 2008-12-29 is 2008-W00-
  • 2008-12-31 is 2008-W00-
  • 2009-01-01 is 2009-W00-
  • 2009-12-31 is 2009-W00- (ISO year 2009 is a leap year, extending the Gregorian year 2009, which starts and ends with Thursday, at both ends with three days)
  • 2010-01-03 is 2010-W00-

Examples where the ISO year is three days into the next gregorian year

  • {{ ISOWEEKDATE|in week case 0|12|31}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|1|1}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|1|2}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|1|3}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|1|4}} gives "|"

Examples where the ISO year is three days into the previous gregorian year

  • {{ ISOWEEKDATE|in week case 0|12|28}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|12|29}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|12|30}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|12|31}} gives "|"
  • {{ ISOWEEKDATE|in week case 0|1|1}} gives "|"
The system does not need the concept of month and is not well connected with the Gregorian system of months: some months January and December are divided over two ISO years.

Week number

Overview of dates with a fixed week number in any year other than a leap year starting on Thursday:

JanuaryJanuary 4th, 11th, 18th, & 25th wk 1-4
FebruaryFebruary 1st, 8th, 15th, & 22nd wk 5-8
MarchMarch 1st, 8th, 14th, 22nd, & 29th wk 9-13
AprilApril 5th, 12th, 19th, & 26th wk 14-17
MayMay 3rd, 10th, 17th, 24th, & 31st wk 18-22
JuneJune 7th, 14th, 21st, & 28th wk 23-26
JulyJuly 5th, 12th, 19th, & 26th wk 27-30
AugustAugust 2nd, 9th, 16th, 23rd, & 30th wk 31-35
SeptemberSeptember 6th, 13rd, 20th, & 27th wk 36-39
OctoberOctober 4th, 11th, 18th, 25th wk 40-43
NovemberNovember 1st, 8th, 15th, 22nd, & 29th wk 44-48
DecemberDecember 6th, 13th, 20th, & 27th wk 49-52


The day of the week for these days are related to Doomsday because for any year, the Doomsday is the day of the week that the last day of February falls on. These dates are one day after the Doomsdays, except that in January and February of leap years the dates themselves are Doomsdays. In leap years the week number is the rank number of its Doomsday.

Advantages

  • The date directly tells the weekday.
  • All years start with a Monday and end with a Sunday.
  • When used by itself without using the concept of month, all years are the same except that leap years have a leap week at the end.
  • The weeks are the same as in the Gregorian calendar.

Disadvantages

Each equinox and solstice varies over a range of at least seven days. This is because each equinox and solstice may occur any day of the week and hence on at least seven different ISO week dates. For example, there are spring equinoxes on 2004-W12-7 and 2010-W11-7.

It cannot replace the Gregorian calendar, because it relies on it to define the new year day (Week 1 Day 1).

Not all parts of the world have a work week that begins with Monday. For example, in some Muslim countries, the work week may begin on Saturday while in other Muslim countries it may begin on Sunday.

The leap year cycle

Below is the 400-year cycle of years in terms of the dominical letter of the year as shown on the right. The three types of week leap year are D, DC, and ED.

Dominical
letter		Doomsday
A or BATuesday
B or CBMonday
C or DCSunday
D or EDSaturday
E or FEFriday
F or GFThursday
G or AGWednesday
,
,
,
,
, |1600|1700|1800|1900| |2000|2100|2200|2300| ,
+
+
+
+
| | 00| BA | C | E | G |+
+
+
+
| |85 57 29 01| G | B | | F | |86 58 30 02| F | A | C | E | |87 59 31 03| E | G | B | | |88 60 32 04|| FE | AG | CB |+
+
+
+
| |89 61 33 05| B | | F | A | |90 62 34 06| A | C | E | G | |91 63 35 07| G | B | | F | |92 64 36 08| FE | AG | CB ||+
+
+
+
| |93 65 37 09| | F | A | C | |94 66 38 10| C | E | G | B | |95 67 39 11| B | | F | A | |96 68 40 12| AG | CB || GF |+
+
+
+
| |97 69 41 13| F | A | C | E | |98 70 42 14| E | G | B | | |99 71 43 15| | F | A | C | | 72 44 16| CB || GF | BA |+
+
+
+
| | 73 45 17| A | C | E | G | | 74 46 18| G | B | | F | | 75 47 19| F | A | C | E | | 76 48 20|| GF | BA ||+
+
+
+
| | 77 49 21| C | E | G | B | | 78 50 22| B | | F | A | | 79 51 23| A | C | E | G | | 80 52 24| GF | BA || FE |+
+
+
+
| | 81 53 25| E | G | B | | | 82 54 26| | F | A | C | | 83 55 27| C | E | G | B | | 84 56 28| BA || FE | AG | '
+
+
+
+
| |1600|1700|1800|1900| |2000|2100|2200|2300| '
'
'
'
'

Thus the ISO leap years in one 400-year cycle are (with this time the 28-year subcycles arranged horizontally):

D ED D DC D

1903 1908 1914 1920 1925 1931 1936 1942 1948 1953 1959 1964 1970 1976 1981 1987 1992 1998 2004 2009 2015 2020 2026 2032 2037 2043 2048 2054 2060 2065 2071 2076 2082 2088 2093 2099 2105 2111 2116 2122 2128 2133 2139 2144 2150 2156 2161 2167 2172 2178 2184 2189 2195 2201 2207 2212 2218 2224 2229 2235 2240 2246 2252 2257 2263 2268 2274 2280 2285 2291 2296

There are 13 28-year subcycles with 5 leap years each, and 6 remaining leap years in the remaining 36 years (the absence of leap days in the Gregorian calendar in 2100, 2200, and 2300 interrupts the subcycles). The leap years are 27 times 5 years apart, 43 times 6 years, and once 7 years. (A slightly more even distribution would be possible: 26 times 5 years apart, and 45 times 6 years.)

The Gregorian years corresponding to the 71 ISO leap years can be subdivided as follows: Thus 27 ISO years are 5 days longer than the corresponding Gregorian year, and 44 are 6 days longer. Of the other 329 Gregorian years (neither starting nor ending with Thursday), 70 are Gregorian leap years, and 259 are non-leap years, so 70 ISO years are 2 days shorter, and 259 are 1 day shorter.

Other week numbering systems

For an overview of week numbering systems see week number. The US system has weeks from Sunday through Saturday, and partial weeks at the beginning and the end of the year. An advantage is that no separate year numbering like the ISO year is needed, while correspondence of lexicographical order and chronological order is preserved.

See Also

External links

Calendars

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Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar. In China today, the Gregorian calendar is used for most day to day activities, but the Chinese calendar is still used for marking traditional Chinese holidays such
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Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwīm al-hijrī
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Gregorian calendar is the most widely used calendar in the world. A modification of the Julian calendar, it was first proposed by the Calabrian doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on 24 February 1582 via the papal bull
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Astronomical year numbering is based on AD/CE year numbering, but follows normal decimal integer numbering more strictly. Thus, it has a year 0 and the years before that are designated with a minus sign '−'. The era designations AD/CE are dropped.
..... Click the link for more information.
Revised Julian calendar or, less formally, New Calendar, is a calendar scheme, originated in 1923, which effectively discontinued the 340 years of divergence between the naming of dates sanctioned by those Eastern Orthodox churches adopting it and the Gregorian calendar
..... Click the link for more information.
lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year. If the solar year is defined as a tropical year then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year then the
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solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere).
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lunar calendar is a calendar in many cultures that is oriented at the moon phase.

This is normally done by having a month which corresponds to a lunation so that the day of month indicates the moon phase. If a calendar tracks the seasons, it is also a lunisolar calendar.
..... Click the link for more information.
Armenian calendar uses the Armenian numerals. It begins in AD 552 as the start of the Armenian era.

Dates are marked by the letters ԹՎ
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Bengali calendar (Bengali: বঙ্গাব্দ Bônggabdo or বাংলা সন Bangla Shôn
..... Click the link for more information.
Berber calendar is the annual calendar used by Berber people in North Africa. This calendar is also known in Arabic under the name of فلاحي fellāḥī "agricultural" or عجمي ajamī "not Arabic".
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Buddhist calendar is used on mainland Southeast Asia in the countries of Cambodia, Laos, Thailand, Myanmar (formerly Burma) and Sri Lanka in several related forms. It is a lunisolar calendar having months that are alternately 29 and 30 days, with an intercalated day and a 30-day
..... Click the link for more information.
Coptic calendar, also called the Alexandrian calendar, is used by the Coptic Orthodox Church. This calendar is based on the ancient Egyptian calendar. To avoid the calendar creep of the latter, a reform of the ancient Egyptian calendar was introduced at the time of Ptolemy
..... Click the link for more information.
Ethiopian calendar (Amharic: የኢትዮጵያ ዘመን አቆጣጠር ye'Ītyōṗṗyā zemen āḳoṭaṭer), also called the
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Germanic calendars were the regional agricultural almanacs in use amongst the Germanic peoples, prior to the adoption of the Julian and later the Gregorian calendar.
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Hebrew calendar (Hebrew: הלוח העברי‎) or Jewish calendar is the calendar used by Jews for religious purposes.
..... Click the link for more information.
Hindu calendar used in ancient times has undergone many changes in the process of regionalization, and today there are several regional Indian calendars, as well as an Indian national calendar. In Pakistan it is called 'desi' or native calendar.
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Indian national calendar (sometimes called Saka calendar) is the official civil calendar in use in India. It is used, alongside the Gregorian calendar, by the Gazette of India, news broadcasts by All India Radio, and calendars and communications issued by the Government of
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Iranian calendar (Persian: سالنمای هجری خورشیدی) also known as Persian calendar or the Jalāli Calendar
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Irish calendar does not observe the typical astronomical seasons (beginning, in the Northern Hemisphere, on the equinoxes and solstices), or the meteorological seasons (beginning on March 1, June 1, September 1 and December 1), but rather centres the seasons around the solstices
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1948 - The following national holidays were introduced: New Year's Day, Coming-of-Age Day, Constitution Memorial Day, Children's Day, Autumnal Equinox Day, Culture Day, Labour Thanksgiving Day.
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This article or section may be confusing or unclear for some readers.
Please [improve the article] or discuss this issue on the talk page. This article has been tagged since December 2006.
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Malayalam calendar (also known as Malayalam Era or Kollavarsham) is a solar Sidereal calendar used in the state of Kerala in South India. The Era started in the year 825 AD.
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The Maya calendar is a system of distinct calendars and almanacs used by the Maya civilization of pre-Columbian Mesoamerica, and by some modern Maya communities in highland Guatemala.
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Nanakshahi (Punjabi: ਨਾਨਕਸ਼ਾਹੀ,
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Bikram Samwat (Bikram Sambat, Devnagari:बिक्रम संवत, abbreviated "B.S.") is the calendar established by Indian emperor Vikramaditya. It is official calendar of Nepal.
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Nepal Sambat (Nepal Bhasa: नेपाल सम्बत) is a lunar calendar. It was initiated by Sankhadhar Sakhwa to commemorate the pay back of all the debts of Nepalese people.
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Tamil Calendar is used in Tamil Nadu in India, and by the Tamil population in Malaysia, Singapore and Sri Lanka. Its use is now largely restricted to cultural and religious events, with the Gregorian calendar having supplanted it for official use both within and outside India.
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Thai lunar calendar or Patitin Chantarakati (Thai: ปฏิทินจันทรคติ) was replaced by the Thai solar calendar Patitin Suriyakati
..... Click the link for more information.


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