Week

For other uses, seeWeek (disambiguation),Weeks (disambiguation),andWeekly (disambiguation).

Aweekis a unit of time equal to sevendays.It is the standard time period used for short cycles of days in most parts of the world. The days are often used to indicate common work days and rest days, as well as days ofworship.Weeks are often mapped against yearlycalendars,but are typically not the basis for them, as weeks are not based on astronomy.

Ancient cultures had different "week" lengths, including ten in Egypt and an eight-day week forEtruscans.The Etruscan week was adopted by theancient Romans,but they later moved to a seven-day week, which had spread across Western Asia and the Eastern Mediterranean due to the influence of the Christian seven-day week, which is rooted in the Jewish seven-day week. In 321 CE, EmperorConstantine the Greatofficially decreed a seven-day week in the Roman Empire, including making Sunday a public holiday.This later spread across Europe, then the rest of the world.

World map showing the first day of the week used in different countries according to theCommon Locale Data Repository

Monday

Friday

Saturday

Sunday

In English, thenames of the days of the weekareMonday,Tuesday,Wednesday,Thursday,Friday,Saturday,andSunday.Sunday, Monday and Saturday are named after celestial bodies in the solar system. The other four days are named after Germanic gods. In many languages, the days of the week are named after gods or classical planets. Such a week may be called aplanetary week(i.e., a classical planetary week).Certain weeks within ayearmay be designated for a particular purpose, such asGolden Week in ChinaandJapan,andNational Family Weekin Canada. More informally, certain groups may advocateawareness weeks,which are designed to draw attention to a certain subject or cause. The term "week" may also be used to refer to a sub-section of the week, such as theworkweek and weekend.

Cultures vary in which days of the week are designated the first and the last, though virtually all have Saturday, Sunday or Monday as the first day. TheGeneva-based ISO standards organization uses Monday as the first day of the week in itsISO week datesystem through the internationalISO 8601standard.Most of Europe and China consider Monday the first day of the (work) week, while North America, Israel, South Asia, and many Catholic and Protestant countries, consider Sunday the first day of the week. Saturday is judged as the first day of the week in much of theMiddle EastandNorth Africadue to the Islamic influence.Other regions are mixed, but typically observe either Sunday or Monday as the first day.

The threeAbrahamic religionsobserve different days of the week as their holy day.Jewsobserve theirSabbath(Shabbat) on Saturday, the seventh day, from sundown Friday to sundown Saturday, in honor of God'screationof the world in six days and then resting on the seventh. MostChristiansobserve Sunday (theLord's Day), the first day of the week in traditional Christian calendars, in honor of theresurrection of Jesus.Muslimsobserve their"day of congregation",known asyaum al-jum`ah,on Friday because it was described as a sacred day of congregational worship in theQuran.

Name

The English wordweekcomes from theOld Englishwice,ultimately from aCommon Germanic*wikōn-,from a root*wik-"turn, move, change". The Germanic word probably had a wider meaning prior to the adoption of theRoman calendar,perhaps "succession series", as suggested byGothicwikōtranslatingtaxis"order" inLuke1:8.

The seven-day week is named in many languages by a word derived from "seven". Thearchaismsennight( "seven-night" ) preserves the old Germanic practice of reckoning time by nights, as in the more commonfortnight( "fourteen-night" ).Hebdomadandhebdomadal weekboth derive from theGreekhebdomás(ἑβδομάς,"a seven" ).Septimanais cognate with theRomanceterms derived fromLatinseptimana( "seven mornings" ).

Slavic has a formation*tъ(žь)dьnь(Serbianтједан,tjedan,Croatiantjedan,Ukrainianтиждень,tyzhden,Czechtýden,Polishtydzień), from *tъ "this" + *dьnь "day". Chinese hasCuối tuần,as it were "planetarytime unit". An older Chinese form isTuần,meaning "week, religious ceremony."

Definition and duration

A week is defined as an interval of exactly sevendays,so that, except when passing throughdaylight saving timetransitions orleap seconds,

1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds.

With respect to theGregorian calendar:

• 1 Gregorian calendar year = 52 weeks + 1 day (2 days in aleap year)
• 1 week =1600⁄6957≈ 22.9984% of an average Gregorian month

In aGregorianmean year, there are 365.2425 days, and thus exactly52+71⁄400or 52.1775 weeks (unlike theJulian yearof 365.25 days or52+5⁄28≈ 52.1786 weeks, which cannot be represented by a finite decimal expansion). There are exactly 20,871 weeks in 400 Gregorian years, so 16 July 1624 was a Tuesday just as was 16 July 2024.

Relative to the path of theMoon,a week is 23.659% of an averagelunationor 94.637% of an average quarter lunation.

Historically, the system ofdominical letters(letters A to G identifying the weekday of the first day of a given year) has been used to facilitatecalculation of the day of week. The day of the week can be easily calculated given a date'sJulian day number(JD, i.e. the integer value atnoonUT): Adding one to theremainderafter dividing the Julian day number by seven (JDmodulo7 + 1) yields that date'sISO 8601day of the week. For example, the Julian day number of 16 July 2024 is 2460508. Calculating2460508 mod 7 + 1yields 2, corresponding to Tuesday.In 1973,John Conwaydevised theDoomsday rulefor mental calculation of the weekday of any date in any year.

Days of the week

Main article:Names of the days of the week

An Italiancameobracelet representing the days of the week by their eponymous deities (mid-19th century,Walters Art Museum)

Schematic comparison of the ordering of the classical planets (arranged in a circle) and the sequence of days in the week (forming a {7/3}heptagramwithin the circle).

The days of the week were named for the sevenclassical planets,which included the Sun and Moon. This naming system persisted alongside an "ecclesiastical" tradition of numbering the days inecclesiastical Latinbeginning withDominica(theLord's Day) as the first day. The Greco-Roman gods associated with the classical planets were rendered in theirinterpretatio germanicaat some point during the late Roman Empire, yielding the Germanic tradition of names based on indigenous deities.

The ordering of the weekday names is not the classical order of the planets (by distance in theplanetary spheresmodel, nor, equivalently, by their apparent speed of movement in the night sky). Instead, theplanetary hourssystems resulted in succeeding days being named for planets that are three places apart in their traditional listing. This characteristic was apparently discussed inPlutarchin a treatise written in c. 100 CE, which is reported to have addressed the question ofWhy are the days named after the planets reckoned in a different order from the actual order?(the text of Plutarch's treatise has been lost).Dio Cassius(early 3rd century) gives two explanations in a section of hisHistoria Romanaafter mentioning the Jewish practice of sanctifying the day called the day ofKronos(Saturday).

	Sunday	Monday	Tuesday	Wednesday	Thursday	Friday	Saturday
Planet	Sun	Moon	Mars	Mercury	Jupiter	Venus	Saturn
Greco-Roman deity	Helios-Sol	Selene-Luna	Ares-Mars	Hermes-Mercury	Zeus-Jupiter	Aphrodite-Venus	Cronus-Saturn
Greek:	ἡμέρα Ἡλίου	ἡμέρα Σελήνης	ἡμέρα Ἄρεως	ἡμέρα Ἑρμοῦ	ἡμέρα Διός	ἡμέρα Ἀφροδίτης	ἡμέρα Κρόνου
Latin:	dies Sōlis	dies Lūnae	dies Martis	dies Mercuriī	dies Iovis	dies Veneris	dies Saturnī
interpretatio germanica	Sun	Moon	Tiwaz	Wodanaz	Þunraz	Frige	—
Old English	sunnandæg	mōnandæg	tiwesdæg	wōdnesdæg	þunresdæg	frīgedæg	sæterndæg
IndianNavagraha	Suryavāra/ Ravivāra/Bhānuvāsara/Ādityavāra	Chandravāra/ Somavāra/ Induvāsara	Mangalavāra/ Bhaumavāsara	Budhavāra/ Saumyavāsara	Guruvāra/Bṛhaspativāsara	Shukravāra/Bhṛguvāsara	Shanivāra/ Sthiravāsara

An ecclesiastical, non-astrological, system of numbering the days of the week was adopted in Late Antiquity. This model also seems to have influenced (presumably viaGothic) the designation of Wednesday as "mid-week" inOld High German(mittawehha) andOld Church Slavonic(срѣда). Old Church Slavonic may have also modeled the name of Monday,понєдѣльникъ,after the Latinferia Secunda.The ecclesiastical system became prevalent inEastern Christianity,but in theLatin Westit remains extant only in modernIcelandic,Galician,andPortuguese.

	"First Day" or "Lord's Day" (Sunday)	"Second Day" (Monday)	"Third Day" (Tuesday)	"Fourth Day" (Wednesday)	"Fifth Day" (Thursday)	"Sixth Day" (Friday)	"Seventh Day" or "Sabbath" (Saturday)
Greek	Κυριακὴ ἡμέρα /kiriaki iméra/	Δευτέρα ἡμέρα /devtéra iméra/	Τρίτη ἡμέρα /tríti iméra/	Τετάρτη ἡμέρα /tetárti iméra/	Πέμπτη ἡμέρα /pémpti iméra/	Παρασκευὴ ἡμέρα /paraskevi iméra/	Σάββατον /sáb:aton/
Latin	[dies] dominica; rarelyferia prima, feria dominica	feria secunda	feria tertia	feria quarta; rarelymedia septimana	feria quinta	feria sexta	Sabbatum; dies sabbatinus, dies Sabbati; rarelyferia septima, feria Sabbati
Hebrew	Hebrew:יום ראשון,romanized:Yom rishon,lit. 'first day'	Hebrew:יום שני,romanized:Yom sheni,lit. 'second day'	Hebrew:יום שלישי,romanized:Yom shlishi,lit. 'third day'	Hebrew:יום רביעי,romanized:Yom revi'i,lit. 'fourth day'	Hebrew:יום חמישי,romanized:Yom chamishi,lit. 'fifth day'	Hebrew:יום שישי,romanized:Yom shishi,lit. 'sixth day'	Hebrew:שבת,romanized:Shabbat,lit. 'Rest/cessation'

History

Circular diagrams showing the division of the day and of the week, from aCarolingianms. (Clm14456 fol. 71r) ofSt. Emmeram Abbey.The week is divided into seven days, and each day into 24 hours, 96puncta(quarter-hours), 240minuta(tenths of an hour) and 960momenta(40th parts of an hour).

Ancient Near East

The earliest evidence of an astrological significance of a seven-day period is connected toGudea,the priest-king ofLagashinSumerduring theGutian dynasty(about 2100 BCE), who built a seven-room temple, which he dedicated with a seven-day festival. In the flood story of theAssyro-BabylonianEpic of Gilgamesh,the storm lasts for seven days, the dove is sent out after seven days (similarly to Genesis), and theNoah-like character ofUtnapishtimleaves the ark seven days after it reaches the firm ground.

Counting from thenew moon,the Babylonians celebrated the 7th, 14th, 21st and 28th of the approximately 29- or 30-day lunar month as "holy days", also called "evil days" (meaning inauspicious for certain activities). On these days, officials were prohibited from various activities and common men were forbidden to "make a wish", and at least the 28th was known as a "rest day". On each of them, offerings were made to a different god and goddess. Though similar, the later practice of associating days of the week with deities or planets is not due to the Babylonians.

Judaism

A continuous seven-day cycle that runs throughout history without reference to the phases of the moon was first practiced inJudaism,dated to the 6th century BCE at the latest.

There are several hypotheses concerning the origin of thebiblicalseven-day cycle.

Friedrich Delitzschand others suggested that the seven-day week being approximately a quarter of alunationis the implicit astronomical origin of the seven-day week,and indeed theBabylonian calendarusedintercalarydays to synchronize the last week of a month with the new moon.According to this theory, the Jewish week was adopted from the Babylonians while removing the moon-dependency.

George Aaron Bartonspeculated that the seven-day creation account of Genesis is connected to the Babylonian creation epic,Enûma Eliš,which is recorded on seven tablets.

In a frequently-quoted suggestion going back to the early 20th century,the HebrewSabbathis compared to the Sumeriansa-bat"mid-rest", a term for thefull moon.The Sumerian term has been reconstructed as renderedSapattu^morSabattu^minBabylonian,possibly present in the lost fifth tablet of theEnûma Eliš,tentatively reconstructed"[Sa]bbath shalt thou then encounter, mid[month]ly".

However,Niels-Erik Andreasen,Jeffrey H. Tigay,and others claim that theBiblical Sabbathis mentioned as a day of rest in some of the earliest layers of thePentateuchdated to the 9th century BCE at the latest, centuries before theBabylonian exile of Judah.They also find the resemblance between the Biblical Sabbath and the Babylonian system to be weak. Therefore, they suggest that the seven-day week may reflect an independentIsraelitetradition.Tigay writes:

It is clear that among neighboring nations that were in position to have an influence over Israel – and in fact which did influence it in various matters – there is no precise parallel to the Israelite Sabbatical week. This leads to the conclusion that the Sabbatical week, which is as unique to Israel as the Sabbath from which it flows, is an independent Israelite creation.

The seven-day week seems to have been adopted, at different stages, by thePersian Empire,inHellenistic astrology,and (viaGreek transmission) inGupta IndiaandTang China. The Babylonian system was received by the Greeks in the 4th century BCE (notably viaEudoxus of Cnidus). Although some sources, such as the Encyclopædia Britannica,state that the Babylonians named the days of the week after the five planets, the sun, and the moon, many scholars disagree.Eviatar Zerubavelsays, "the establishment of a seven-day week based on the regular observance of the Sabbath is a distinctively Jewish contribution to civilization. The choice of the number 7 as the basis for the Jewish week might have had an Assyrian or Babylonian origin, yet it is crucial to remember that the ancient dwellers of Mesopotamia themselves did not have a seven-day week."The astrological concept ofplanetary hoursis an innovation of Hellenistic astrology, probably first conceived in the 2nd century BCE.

The seven-day week was widely known throughout theRoman Empireby the 1st century CE,along with references to the Jewish Sabbath by Roman authors such asSenecaandOvid.When the seven-day week came into use in Rome during the early imperial period, it did not immediately replace the older eight-daynundinalsystem.The nundinal system had probably fallen out of use by the time EmperorConstantineadopted the seven-day week for official use in CE 321, making theDay of the Sun(dies Solis) a legal holiday.

Achaemenid period

TheZoroastrian calendarfollows the Babylonian in relating the 7th, 14th, 21st, and 28th of the 29- or 30-day lunar month toAhura Mazda. The forerunner of all modern Zoroastrian calendars is the system used to determine dates in thePersian Empire,adopted from the Babylonian calendar by the 4th century BCE.

Frank C. Sennin his bookChristian Liturgy: Catholic and Evangelicalpoints to data suggesting evidence of an early continuous use of a seven-day week; referring to the Jews during theBabylonian captivityin the 6th century BCE,after the destruction of theTemple of Solomon. While the seven-day week in Judaism is tied toCreation accountin theBook of Genesisin theHebrew Bible(whereGodcreates the heavens and the earth in six days and rests on the seventh; Genesis 1:1-2:3,in theBook of Exodus,the fourth of theTen Commandmentsis to rest on the seventh day,Shabbat,which can be seen as implying a socially instituted seven-day week), it is not clear whether the Genesis narrative predates theBabylonian captivityof the Jews in the 6th century BCE. At least since theSecond Temple periodunder Persian rule, Judaism relied on the seven-day cycle of recurringSabbaths.

Tabletsfrom the Achaemenid period indicate that thelunationof 29 or 30 days basically contained three seven-day weeks, and a final week of eight or nine days inclusive, breaking the continuous seven-day cycle. The Babylonians additionally celebrated the 19th as a special "evil day", the "day of anger", because it was roughly the 49th day of the (preceding) month, completing a "week of weeks", also with sacrifices and prohibitions.

Difficulties withFriedrich Delitzsch'sorigin theoryconnecting HebrewShabbatwith the Babylonianlunar cycleinclude reconciling the differences between an unbroken week and a lunar week, and explaining the absence of texts naming the lunar week asShabbatin any language.

Hellenistic and Roman era

Main article:Nundinae

InJewish sourcesby the time of theSeptuagint,the term "Sabbath" (Greek:Σάββατον,romanized:Sábbaton) bysynecdochealso came to refer to an entire seven-day week,the interval between two weekly Sabbaths.Jesus's parableof thePharisee and the Publican(Luke 18:12) describes the Pharisee as fasting "twice in the week" (Greek:δὶς τοῦ σαββάτου,romanized:dis tou sabbatou). In the account of the women finding the tomb empty, they are described as coming there "toward the one of the sabbaths" (Greek:εἰς μίαν σαββάτων, τῇ μιᾷ τῶν σαββάτων);translations substitute "week" for "sabbaths".

The ancient Romans traditionally used the eight-daynundinumbut, after theJulian calendarhad come into effect in 45 BCE, the seven-day week came into increasing use. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted byConstantinein 321 CE, the nundinal cycle had fallen out of use. The association of thedays of the weekwith the Sun, the Moon and the five planets visible to the naked eye dates to theRoman era(2nd century).

The continuous seven-day cycle of the days of the week can be traced back to the reign ofAugustus;the first identifiable date cited complete withday of the weekis 6 February 60 CE, identified as a "Sunday"(asviii idus Februarius dies solis"eighth day before the ides of February, day of the Sun" ) in a Pompeiian graffito. According to the (contemporary) Julian calendar, 6 February 60 was, however, aWednesday.This is explained by the existence of two conventions of naming days of the weeks based on theplanetary hourssystem: 6 February was a "Sunday" based on the sunset naming convention, and a "Wednesday" based on the sunrise naming convention.

Islamic concept

According to Islamic beliefs, the seven-day a week concept started with the creation of the universe by Allah.Abu Hurairareported thatMuhammadsaid: Allah, the Exalted and Glorious, created the clay on Saturday and He created the mountains on Sunday and He created the trees on Monday and He created the things entailing labour on Tuesday and created light on Wednesday and He caused the animals to spread on Thursday and created Adam after 'Asr on Friday; the last creation at the last hour of the hours of Friday, i. e. between afternoon and night.

Adoption in Asia

China and Japan

The earliest known reference in Chinese writings to a seven-day week is attributed to Fan Ning, who lived in the late 4th century in theJin dynasty,while diffusions from theManichaeansare documented with the writings of the Chinese Buddhist monkYi Jingand the Ceylonese or Central Asian Buddhist monkBu Kongof the 7th century (Tang dynasty).

The Chinese variant of the planetary system was brought to Japan by the Japanese monkKūkai(9th century). Surviving diaries of the Japanese statesmanFujiwara Michinagashow the seven-day system in use inHeian PeriodJapan as early as 1007. In Japan, the seven-day system was kept in use for astrological purposes until its promotion to a full-fledged Western-style calendrical basis during theMeiji Period(1868–1912).

India

The seven-day week was known in India by the 6th century, referenced in thePañcasiddhāntikā.Shashi (2000) mentions theGarga Samhita,which he places in the 1st century BCE or CE, as a possible earlier reference to a seven-day week in India. He concludes "the above references furnish aterminus ad quem(viz. 1st century) Theterminus a quocannot be stated with certainty ".

Christian Europe

Further information:Holy WeekandEaster Week

The seven-day weekly cycle has remained unbroken inChristendom,and hence inWestern history,for almost two millennia, despite changes to theCoptic,Julian,andGregoriancalendars, demonstrated by the date ofEasterSunday having been traced back through numerouscomputistic tablesto an Ethiopic copy of an early Alexandrian table beginning with the Easter of 311 CE.

A tradition of divinations arranged for the days of the week on which certain feast days occur develops in the Early Medieval period. There are many later variants of this, including the GermanBauern-Praktikand the versions ofErra Paterpublished in 16th to 17th century England, mocked inSamuel Butler'sHudibras.South and East Slavic versions are known askoliadniki(fromkoliada,a loan of Latincalendae), with Bulgarian copies dating from the 13th century, and Serbian versions from the 14th century.

Medieval Christian traditions associated with the lucky or unlucky nature of certain days of the week survived into the modern period. This concerns primarilyFriday,associated with thecrucifixion of Jesus.Sunday,sometimes personified asSaint Anastasia,was itself an object of worship in Russia, a practice denounced in a sermon extant in copies going back to the 14th century.

Sunday,in the ecclesiastical numbering system also counted as theferia primaor the first day of the week; yet, at the same time, figures as the "eighth day",and has occasionally been so called in Christian liturgy.

Justin Martyrwrote: "the first day after the Sabbath, remaining the first of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first."

A period of eight days, usually (but not always, mainly because of Christmas Day) starting and ending on a Sunday, is called anoctave,particularly inRoman Catholic liturgy.In German, the phraseheute in acht Tagen(literally "today in eight days" ) can also mean one week from today (i.e. on the same weekday). The same is true of the Italian phraseoggi otto(literally "today eight" ), the Frenchà huitaine,and the Spanishde hoy en ocho.

Numbering

Further information:Leap week calendar

Weeks in a Gregorian calendar year can be numbered for each year. This style of numbering is often used in European and Asian countries. It is less common in the U.S. and elsewhere.

The ISO week date system

The system for numbering weeks is theISO week datesystem, which is included inISO 8601.This system dictates that each week begins on a Monday and is associated with the year that contains that week's Thursday.

DeterminingWeek 1

In practice week 1 (W01in ISO notation) of any year can be determined as follows:

• If 1 January falls on a Monday, Tuesday, Wednesday or Thursday, then the week of 1 January is Week 1. Except in the case of 1 January falling on a Monday, this Week 1 includes the last day(s) of thepreviousyear.
• If 1 January falls on a Friday, Saturday, or Sunday, then 1 January is considered to be part of the last week of thepreviousyear. Week 1 will begin on the first Monday after 1 January.

Examples:

• Week 1 of 2015 (2015W01in ISO notation) started on Monday, 29 December 2014 and ended on Sunday, 4 January 2015, because 1 January 2015 fell on Thursday.
• Week 1 of 2021 (2021W01in ISO notation) started on Monday, 4 January 2021 and ended on Sunday, 10 January 2021, because 1 January 2021 fell on Friday.

Week 52 and 53

It is also possible to determine if the last week of the previous year was Week 52 or Week 53 as follows:

• If 1 January falls on a Friday, then it is part of Week 53 of the previous year (W53-5).
• If 1 January falls on a Saturday,
  • then it is part of Week 53 of the previous year if that is aleap year(W53-6),
  • and part of Week 52 otherwise (W52-6), i.e. if the previous year is a common year.
• If 1 January falls on a Sunday, then it is part of Week 52 of the previous year (W52-7).

Schematic representation ofISO week date

Dominical letter(s) plus weekdays, dates and week numbers at the beginning and end of a year

Dominical letter(s)1	Days at the start of January							Effect1,2				Days at the end of December1
	1 Mon	2 Tue	3 Wed	4 Thu	5 Fri	6 Sat	7 Sun	W01-13	01 Jan week	...	31 Dec week	1 Mon4	2 Tue	3 Wed	4 Thu	5 Fri	6 Sat	7 Sun
G(F)	01	02	03	04	05	06	07	01 Jan	W01	...	W01	31 (30)	(31)
F(E)		01	02	03	04	05	06	31 Dec	W01	...	W01	30 (29)	31 (30)	(31)
E(D)			01	02	03	04	05	30 Dec	W01	...	W01(W53)	29 (28)	30 (29)	31 (30)	(31)
D(C)				01	02	03	04	29 Dec	W01	...	W53	28 (27)	29 (28)	30 (29)	31 (30)	(31)
C(B)					01	02	03	04 Jan	W53	...	W52	27 (26)	28 (27)	29 (28)	30 (29)	31 (30)	(31)
B(A)						01	02	03 Jan	W52(W53)	...	W52	26 (25)	27 (26)	28 (27)	29 (28)	30 (29)	31 (30)	(31)
A(G)							01	02 Jan	W52	...	W52 (W01)	25 (31)	26 (25)	27 (26)	28 (27)	29 (28)	30 (29)	31 (30)

Notes
1. Numbers and letters in parentheses, ( ), apply to March − December in leap years.
2.Underlinednumbers and letters belong to previous year or next year.
3. First date of thefirstweek in the year.
4. First date of thelastweek in the year.

Other week numbering systems

In some countries, though, the numbering system is different from the ISO standard. At least six numberings are in use:

System	First day of week	First week of year contains			Can be last week of previous year	Used by or in
ISO 8601	Monday	4 January	1st Thursday	4–7 days of year	yes	EU (exc. Portugal) and most of other European countries, most of Asia and Oceania
Middle Eastern	Saturday	1 January	1st Friday	1–7 days of year	yes	Much of the Middle East
Western traditional	Sunday	1 January	1st Saturday	1–7 days of year	yes	Canada, United States, Iceland, Portugal, Japan, Taiwan, Thailand, Hong Kong, Macau, Israel, Egypt, South Africa, the Philippines, and most of Latin America
Broadcast Calendar	Monday	1 January	1st Sunday	1–7 days of year	yes	Broadcast services in the United States

Because the week starts on either Saturday, Sunday, or Monday in all these systems, the days in aworkweek,Monday through Friday, will always have the same week number within a calendar week system. Quite often, these systems will agree on the week number for each day in a workweek:

• In years where 1 January is aMonday,Tuesday,Wednesday,orThursday,all of the above week numbering systems will agree.
• In years where 1 January is a Friday,ISO-8601 will be different, but the rest will agree.
• In years where 1 January is a Saturday,ISO-8601 and the Middle Eastern system will agree, being different from Western Traditional and the Broadcast Calendar which will agree.
• In years where 1 January is a Sunday,the Broadcast Calendar will be different, but the rest will agree.

Note that this agreement occurs only for the week number of each day in a work week, not for the day number within the week, nor the week number of the weekends.

Theepi week(epidemiological week) is used to report healthcare statistics, as with COVID-19 cases:

The epidemiological week begins on Sunday and ends on Saturday. The first epidemiological week of the year ends on the first Saturday of January, provided that it falls at least four or more days into the month. Therefore, the first epidemiological week may actually begin in December of the previous year.

Uses

Thesemiconductor package date codeis often a 4 digit date code YYWW where the first two digits YY are the last 2 digits of the calendar year and the last two digits WW are the two-digit week number.

Thetire date code mandated by the US DOTis a 4 digit date code WWYY with two digits of the week number WW followed by the last two digits of the calendar year YY.

"Weeks" in other calendars

The term "week" is sometimes expanded to refer to other time units comprising a few days. Such "weeks" of between four and ten days have been used historically in various places.Intervals longer than 10 days are not usually termed "weeks" as they are closer in length to thefortnightor themonththan to the seven-day week.

Pre-modern

Calendars unrelated to the Chaldean, Hellenistic, Christian, or Jewish traditions often have time cycles between the day and the month of varying lengths, sometimes also called "weeks".

Aneight-day weekwas used inAncient Romeand possibly in the pre-ChristianCeltic calendar.Traces of a nine-day week are found in Baltic languages and inWelsh.The ancient Chinese calendar had aten-day week,as did the ancientEgyptian calendar(and, incidentally, theFrench Republican Calendar,dividing its 30-day months into thirds).

A six-day week is found in theAkan CalendarandKabiyeculture until 1981. Several cultures used a five-day week, including the 10th centuryIcelandic calendar,theJavanese calendar,and the traditional cycle of market days inKorea.TheIgbohave a "market week" of four days. Evidence of a "three-day week" has been derived from the names of the days of the week inGuipuscoan Basque.

The Aztecs and Mayas used theMesoamerican calendars.The most important of these calendars divided a ritual cycle of 260 days (known asTonalpohualliinNahuatlandTzolk'ininYucatec Maya) into 20 weeks of 13 days (known in Spanish astrecenas). They also divided the solar year into 18 periods (winal) of 20 days and five nameless days (wayebʼ), creating a 20-day month divided into four five-day weeks. The end of each five-day week was a market day.

The BalinesePawukonis a 210-day calendar consisting of 10 different simultaneously running weeks of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 days, of which the weeks of 4, 8, and 9 days are interrupted to fit into the 210-day cycle.

Modern reforms

Further information:Decimal calendar,French Revolutionary Calendar § Ten days of the week,Bahá'í calendar,International Fixed Calendar,andSoviet calendar

TheInternational Fixed Calendar(also known as the "Eastman plan" ) kept a 7-day week while defining a year of 13 months with 28 days each (364 days). Every calendar date was always on the same weekday. It was the official calendar of theEastman Kodak Companyfor decades.

A 10-day week, called adécade,was used in France for nine and a half years from October 1793 to April 1802; furthermore, theParis Communeadopted the Revolutionary Calendar for 18 days in 1871.

The Bahá'í calendar features a 19-day period which some classify as a month and others classify as a week.

Soviet

Soviet calendar, 1930.
Five colors of five-day work week repeat.

Soviet calendar, 1933.
Rest day of six-day work week in blue.

Days of each Gregorian month in both calendars are grouped vertically into seven-day weeks.

In theSoviet Unionbetween 1929 and 1940, most factory and enterprise workers, but not collective farm workers, used five and six day work weeks while the country as a whole continued to use the traditional seven day week.

From 1929 to 1951, five national holidays were days of rest (22 January,1–2 May,7–8 November). From autumn 1929 to summer 1931, the remaining 360 days of the year were subdivided into 72 five day work weeks beginning on1 January.Workers were assigned any one of the five days as their day off, even if their spouse or friends might be assigned a different day off. Peak use of the five day work week occurred on1 October 1930at 72% of industrial workers. From summer 1931 until26 June 1940,each Gregorian month was subdivided into five six day work weeks, more-or-less, beginning with the first day of each month. The sixth day of each six day work week was a uniform day of rest. On1 July 193574.2% of industrial workers were on non-continuous schedules, mostly six day work weeks, while 25.8% were still on continuous schedules, mostly five day work weeks. The Gregorian calendar with its irregular month lengths and the traditional seven day week were used in the Soviet Union during its entire existence, including 1929–1940; for example, in the masthead ofPravda,the official Communist newspaper, and in both Soviet calendars displayed here. The traditional names of the seven day week continued to be used, including "Resurrection" (Воскресенье) for Sunday and "Sabbath" (Суббота) for Saturday, despite the government'sofficialatheism.

See also

• Determination of the day of the week
• GPS week number
• Names of the days of the week
• Workweek and weekend

References

• Zerubavel, Eviatar (1989).The Seven Day Circle: The History and Meaning of the Week.University of Chicago Press.ISBN978-0-226-98165-9.

Further reading

• Colson, Francis Henry (1926).The Week: An Essay on the Origin and Development of the Seven-day Cycle.Cambridge University Press.OCLC59110177.
• Thomas, Northcote Whitridge(1911)."Week".InChisholm, Hugh(ed.).Encyclopædia Britannica.Vol. 28 (11th ed.). Cambridge University Press. p. 466.