Seven-day week

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For more information on other weeks, see Week. For more information on each day of the week, see Names of the days of the week.
See also: Planetary hours

The seven-day week is used by the majority of the world and is the international standard as specified in ISO 8601.

The word for "week" in different languages[edit]

The seven-day time unit is named in many languages by a word derived from "seven", such as the Latin septimana and its derivates in Romance languages. In English there used to be two options, the word "week" which is of Germanic origin,[1] and a now no longer used composite one, sennight (also sennight or se'night), an abbreviation of "seven-night",[2] which was still in use in the early 19th century, to judge from Jane Austen's letters, and which is comparable in structure to the word "fortnight".


The seven-day week is a time unit which is, unlike the day, month or year, not based on any obvious astronomical phenomenon.[3] However, important seven-star constellations and the discovery of the almost seven-day long lunar phases might well have induced the veneration of the number seven.[4]

The earliest evidence of an astrological significance of a seven-day period is connected to Gudea, priest-king of Lagash in Sumer during the Gutian dynasty, who built a seven-room temple, which he dedicated with a seven-day festival.[4] In the flood story of the Assyro-Babylonian epic of Gilgamesh the storm lasts for seven days, the dove is sent out after seven days, and the Noah-like character of Utnapishtim leaves the ark seven days after it reaches firm ground.[4]

The seven-day week as such was first decreed by King Sargon I of Akkad around 2300 BCE.[5] It seems likely that the Hebrew seven-day week is based on the Babylonian tradition, although going through certain adaptations.[4] The seven-day week was adopted in Hellenistic astrology, possibly directly from Babylonian tradition, and was introduced in the Roman Empire beginning in about the 1st century. It became official part of the Roman calendar by decree in the 4th century under Constantine the Great, and with adoption of Christianity as the Roman state religion later in the 4th century, it also became integral part of the Christian liturgical calendar.[6]

Ancient Near East[edit]

The Babylonian Imago Mundi, dated to the 6th century BCE (Neo-Babylonian Empire).[7] The map shows Babylon on the Euphrates, surrounded by a circular landmass showing Assyria, Armenia and several cities, in turn surrounded by a "bitter river" (Oceanus), with seven islands arranged around it so as to form a seven-pointed star.
Lunation-based theory

Babylonians celebrated a holy day every seven days, starting from the new moon, then the first visible crescent of the Moon, but adjusted the number of days of the final "week" in each month so that months would continue to commence on the new moon. (The seven-day week is only 23.7% of a lunation, so a continuous cycle of seven-day weeks rapidly loses synchronization with the lunation.)

The seven-day week being approximately a quarter of a lunation has been proposed (e.g. by Friedrich Delitzsch) as the implicit, astronomical origin of the seven-day week. Problems with the proposal include lack of synchronization, variation in individual lunar phase lengths, and incompatibility with the duodecimal (base-12) and sexagesimal (base-60) numeral systems, historically the primary bases of other chronological and calendar units. For instance, the Chinese Han Dynasty (from 206 BCE) used five-day and ten-day cycles.


Counting from the new moon, the Babylonians celebrated the 7th, 14th, 21st, and 28th as "holy-days", also called "evil days" (meaning "unsuitable" for prohibited 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".[8] On each of them, offerings were made to a different god and goddess. Tablets from the 6th-century BCE reigns of Cyrus the Great and Cambyses indicate these dates were sometimes approximate. The lunation of 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.[8] 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.[8] Difficulties with Friedrich Delitzsch's origin theory connecting Hebrew Shabbat with the Babylonian lunar cycle[9] include reconciling the differences between an unbroken week and a lunar week, and explaining the absence of texts naming the lunar week as Shabbat in any language.[10] Reconstruction of a broken tablet seems to define the rarely attested Babylonian Akkadian word Sapattum or Sabattum as the full moon: this word is cognate or merged with Hebrew Shabbat, but is monthly rather than weekly. It is regarded as a form of Sumerian sa-bat ("mid-rest"), attested in Akkadian as um nuh libbi ("day of mid-repose").[8] This conclusion is a contextual restoration of the damaged Enûma Eliš creation account, which is read as: "[Sa]bbath shalt thou then encounter, mid[month]ly".[8]

Hebrew Bible

The seven-day week is particularly identified with Judaism: it appears in the Creation account in the Book of Genesis, in the Hebrew Bible, where Elohim (God) creates the heavens and the earth in six days and rests on the seventh (Genesis 1:1-2:3). In the Book of Exodus, the fourth of the Ten Commandments is to rest on the seventh day (Shabbat), which can be seen as implying a socially instituted seven-day week. Most who observe Biblical Sabbath affirm it as having been instituted as a perpetual covenant for the people of Israel (Exodus 31:13-17), a sign respecting two events: the day during which God rested after having completed the Creation in six days (Exodus 20:8-11), and God's deliverance from the Egyptian seven-day workweek (Deuteronomy 5:12-15).

Persian Empire

The Zoroastrian calendar follows the Babylonian in relating the seventh and other days of the month to Ahura Mazda.[11] The forerunner of all modern Zoroastrian calendars is the system used to reckon dates in the Persian Empire, adopted from the Babylonian calendar by the 4th century BC

Classical Antiquity[edit]

By synecdoche (naming a part for the whole), in Jewish sources by the time of the Septuagint, the term "Sabbath" (Greek Sabbaton) also came to mean an entire "se'nnight" or seven-day week,[12] the interval between two weekly Sabbaths. Jesus's parable of the Pharisee and the Publican (Luke 18:12) describes the Pharisee as fasting "twice in the week" (Greek dis tou sabbatou).

Frank C. Senn in his book Christian Liturgy: Catholic and Evangelical points to data suggesting evidence of an early continuous use of a seven-day week; referring to the Jews during the Babylonian Captivity in the 6th century BCE,[13] after the destruction of the Temple of Solomon. The ancient Romans traditionally used the eight-day nundinal cycle, but after the Julian calendar had come into effect in 45 BC, the seven-day week came into use. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted by Constantine in CE 321[14] the nundinal cycle had fallen out of use. The association of the days of the week with the Sun, the Moon, and the five planets visible to the naked eye dates to the Roman era (2nd century).

Christian Europe[edit]

The seven-day weekly cycle has remained unbroken in Europe for almost two millennia, despite changes to the Alexandrian, Julian, and Gregorian calendars, demonstrated by the date of Easter Sunday having been traced back through numerous computistic tables to an Ethiopic copy of an early Alexandrian table beginning with the Easter of 311 AD.[15]

"The Roman context of the spread of Christianity meant that Rome contributed a lot to the structure and calendar of the new faith."[16]

Other systems[edit]


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 the Jin Dynasty, while diffusions from the Manichaeans are documented with the writings of the Chinese Buddhist monk Yi Jing and the Ceylonese or Central Asian Buddhist monk Bu Kong of the 7th century (Tang Dynasty).


The Chinese transliteration of the planetary system was soon brought to Japan by the Japanese monk Kobo Daishi. Surviving diaries of the Japanese statesman Fujiwara Michinaga show the seven-day system in use in Heian Japan 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 the Meiji era.


The seven-day week was known in Indian by the sixth century, referenced in the Pañcasiddhāntikā.[citation needed].

Shashi (2000) mentions the Garga Samhita, which he places in the 1st century BCE, as a possible earlier reference to a seven-day week in India. He concludes "the above references furnish a terminus ad quem (viz. 1st century BCE–1st century CE) The terminus a quo cannot be stated with certainty".[17][18]


France discontinued the seven-day week for a ten-day week with the introduction of the republican calendar in 1793. The Concordat of 1801, which re-established the Roman Catholic Church in France, also restored the seven-day week, beginning with Easter Sunday, 18 April 1802.

Soviet Union[edit]

Main article: Soviet calendar

In 1929, the USSR discontinued the seven-day week for a five-day week, then a six-day week. While the days were still named according to the seven-day week, the work schedules were rotated in five- and six-day periods. The seven-day week was reintroduced on 27 June 1940.

Week numbering[edit]

World map showing first day of week used in different countries
World map showing holidays of week in different countries

Weeks in a Gregorian calendar year can be numbered for each year. This style of numbering is commonly used (for example, by schools and businesses) in some European and Asian countries, but rare elsewhere.

ISO 8601 includes the ISO week date system, a numbering system for weeks – each week begins on a Monday and is associated with the year that contains that week's Thursday (so that if a year starts in a long weekend Friday–Sunday, week number one of the year will start after that). For example, week 1 of 2004 (2004W01) ran from Monday 29 December 2003 to Sunday, 4 January 2004, because its Thursday was 1 January 2004, whereas week 1 of 2005 (2005W01) ran from Monday 3 January 2005 to Sunday 9 January 2005, because its Thursday was 6 January 2005 and so the first Thursday of 2005. The highest week number in a year is either 52 or 53 (it was 53 in the year 2004). Schematically, this ISO convention translates as follows:

Dates in January Effect
M T W T F S S Week number Week assigned to
1 2 3 4 5 6 7 1 New year
1 2 3 4 5 6 1 New year
1 2 3 4 5 1 New year
1 2 3 4 1 New year
1 2 3 53 Previous year
1 2 53 or 52 Previous year
1 52 Previous year

In some countries, though, the numbering system is different from the ISO standard. At least six numberings are in use:[19][20]

System First day of week First week of year contains Can also be last week of previous year Used by/in
ISO-8601 Monday 4 January 1st Thursday 4–7 days of year no                     EU and most of other European countries
(Islamic) Saturday 1 January 1st Friday 1–7 days of year yes Much of the Middle East
(North American) Sunday 1 January 1st Saturday 1–7 days of year yes Canada, USA, Mexico, China, Japan

The semiconductor package date code is 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.[21][22]

The tire date code mandated by the US DOT is 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.[23]

Facts and figures[edit]

  • 1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds (except at daylight saving time transitions or leap seconds)
  • 1 Gregorian calendar year = 52 weeks + 1 day (2 days in a leap year)
  • 1 week = 16006957 ≈ 22.9984% of an average Gregorian month

In a Gregorian mean year there are 365.2425 days, and thus exactly 52 71400 or 52.1775 weeks (unlike the Julian year of 365.25 days or 52 528 ≈ 52.1786 weeks, which cannot be represented by a finite decimal expansion). There are exactly 20871 weeks in 400 Gregorian years, so 30 April 1611 was a Saturday just like 30 April 2011.

A system of Dominical letters has been used to determine the day of week in the Gregorian or the Julian calendar.

See also[edit]


  1. ^ [1]
  2. ^ [2]
  3. ^ [3]
  4. ^ a b c d Leland, S. Copeland (April 1939). "Sources of the Seven-Day Week". Popular Astronomy. Vol. XLVII, No. 4: 176 ff. 
  5. ^ Anthony R. Michaelis. "The Enigmatic Seven". Interdisciplinary Science Reviews (ISR) 7: 373. ... the first great empire builder, King Sargon I of Akkad (2335 to 2279 BC), decreed a seven-day week in his Empire. He lived for 56 years, established the first Semitic Dynasty and defeated the Sumerian City States. Thus the Akkadian language spread, it was adopted by the Babylonians, and the seven-day week was similarly inherited from him. 
  6. ^ Senn, Frank C. (1997). Christian Liturgy: Catholic and Evangelical. Fortress Press. ISBN 9780800627263. 
  7. ^ Siebold, Jim. "Slide 103". Retrieved 2009-01-21. 
  8. ^ a b c d e Pinches, T.G. (2003). "Sabbath (Babylonian)". In Hastings, James. Encyclopedia of Religion and Ethics 20. Selbie, John A., contrib. Kessinger Publishing. pp. 889–891. ISBN 978-0-7661-3698-4. Retrieved 2009-03-17. 
  9. ^ Landau, Judah Leo. The Sabbath. Johannesburg, South Africa: Ivri Publishing Society, Ltd. pp. 2, 12. Retrieved 2009-03-26. 
  10. ^ Sampey, John Richard (1915). "Sabbath: Critical Theories". In Orr, James. The International Standard Bible Encyclopedia. Howard-Severance Company. p. 2630. 
  11. ^ Boyce, Mary (ed. & trans.). Textual Sources for the Study of Zoroastrianism. University of Chicago Press, 1984, p. 19-20.
  12. ^ Strong's Concordance, 4521.
  13. ^ Senn, Frank C. (1997). Christian Liturgy: Catholic and Evangelical. Fortress Press. ISBN 978-0-8006-2726-3. 
  14. ^ Zerubavel, Eviatar (1989). The Seven Day Circle: The History and Meaning of the Week. University of Chicago Press. p. 45. ISBN 978-0-226-98165-9. 
  15. ^ Neugebauer, Otto (1979). Ethiopic astronomy and computus. Verl. d. Österr. Akad. d. Wiss. ISBN 978-3-7001-0289-2. 
  16. ^
  17. ^ Shashi, Shyam Singh (2000). Encyclopaedia Indica India, Pakistan, Bangladesh Vol. 76 Major dynasties of ancient Orissa: India, Pakistan, Bangladesh. Anmol Publications PVT. LTD. pp. 114–115. ISBN 978-81-7041-859-7. 
  18. ^ Kane, Dr. Pandurang Vaman (1930–1962). History of Dharmasastra. 
  19. ^ Weeknumber sorted by definition
  20. ^ Calendar Weeks
  21. ^ "Marking Convention".
  22. ^ "Top Mark Convention - 4-Digit Date Code".
  23. ^ "49 CFR 574.5 - Tire identification requirements.".

External links[edit]