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Online Calendar Converters

Fourmilabs Calendar Converter

Epistime Academy Calendar Converter

Hebrew Calendar Calculator

Chronos - coverts dates in various ancient calendars to Julian Dates

Stern, S. (2012). "Calendars in antiquity : empires, states, and societies.".. S

Chronology of the Ancient World by Bickerman (1980)

Seidelmann, P. K., et al. (1992). Explanatory Supplement to the Astronomical Almanac, University Science Books.


Meeus, 1991 Astronomical Algorithms

Reingold and Dershowitz, Calendrical Calculations: The Ultimate Edition.. RD

Astronomical Calculations: The Julian Day

History of Calendars (Wikipedia)

Grumel, V. (1958). La chronologie, Presses Universitaires de France.. G GE

Grumel, V. (1934). L Annee du Monde dans la Chronographie de Theophane. Echos d Orient 33: 396 - 408.

Other works by Vernace Grumel

Finegan, J. (1998). Handbook of biblical chronology : principles of time reckoning in the ancient world and problems of chronology in the Bible. Peabody, Mass., Hendrickson Publishers.. F98

Research Project on Calendars of Late Antiquity and the Middle Ages at University College London (UCL)

Research Project on the Hemerlogia at University College London (UCL)

Specific Calendars



The Julian Calendar is a solar calendar proposed by Julius Caesar and standardized by Augustus. It was modeled on the ancient Egyptian civil calendar. A normal Julian year has 365 days while leap years, which occur every 4 years, add an additional day to the month of February. No other intercalations are made. 1 January marks the start of a Julian year. By convention, dates before the Gregorian Calendar reform of 1582 CE are reported in the Julian Calendar. A Julian day begins at midnight.

The Julian Calendar - timeanddate.com

Julian Calendar at scienceworld.wolfram.com

Anno Mundi


A.M. – Anno Mundi. This calendar was used by several of the Byzantine authors including Theophanes and Anastasius Bibliothecarius. The calendar is based on the Julian calendar however the year does not begin on 1 January and the starting day, month, and year of this calendar was a point of contention as it was based on an estimate for the start of "creation" (among other things) as interpreted through the Septuagint - a Greek translation of the Old Testament. An ongoing several hundred year long theological debate over when Biblical "creation" began led to multiple versions of the A.M. calendar. The earlier Byzantine sources used the Alexandrian version (A.M.a) or “Alexandrian era” of this calendar which has a starting date of 25 March 5492 BCE or, according to Bickerman (1980), 25 March 5493 BCE. Earthquake catalogers Guidoboni et al (1994) and Ambraseys (2009) assume a starting date of 25 March 5492 BCE and that is what I use. As explained by Grumel (1958:219)

The Alexandrian era of Panodorus began in 5493 BCE [and] the Alexandrian era of Annianos began in 5492 BCE. The Alexandrian Era of Annianos is what is commonly called the Alexandrian era.
Another reckoning system, used for example by Megas Chronographos, is the Byzantine version (A.M.Byz) which has a starting date of 1 September 5509 BCE (Bickerman, 1980:73-74). Yet another reckoning system is a variant suggested in Chronicon Paschale which was composed in ~630 CE. The starting date for this system is 21 March, 5507 BCE. In the Anno Mundi calendar system used by the Byzantine authors, the day followed the Roman civil custom of beginning the calendarical day at midnight. When hours are indicated they mark time since dawn. Hence, if daybreak began at 6 am, the 4th hour would correspond to 10 am (Rautman, 2007:3).

Calendaric Inconsistencies of Individual Authors
Author Inconsistencies
Theophanes Grumel (1934:407), Proudfoot (1974:373-374), and others have pointed out that Theophanes A.M.a in the years A.M.a 6102-6206 and A.M.a 6218-6265 are frequently a year too low.

Byzantine Calendar - wikipedia



Indictions - An indiction (Latin: indictio, impost) was a periodic reassessment of taxation in the Roman Empire which took place every fifteen years. In Late Antiquity, this 15-year cycle began to be used to date documents and it continued to be used for this purpose in Medieval Europe. Indictions refer to an individual year in the 15 year cycle; for example, "the fourth indiction" came to mean the fourth year of the current indiction. Since the cycles themselves were not numbered, other information is needed to identify the specific year. When an ancient author supplies an indiction along with an A.M. date, the result may be greater chronological precision. For our dating purposes, indictions began in 312 CE when they were introduced by the Roman Emperor Constantine. The indiction was first used to date documents unrelated to tax collection in the mid-fourth century. By the late fourth century it was being used to date documents throughout the Mediterranean. In 537 CE, Roman Emperor Justinian decreed that all dates must include the indiction.Outside of Egypt, the year of the indiction generally began on 1 September (Bickerman, 1980:78).

Indictions - wikipedia

Chart of Indictions

Seleucid Era including the Syriac Calendar (A.G. - Anno Graecorum)


The Anno Graecorum (A.G.) Calendar is also known as the Seleucid Era, Chaldean, or the Macedonian Calendar. This calendar began at the start of the Seleucid Empire and was assimilated into the Babylonian calendar with Macedonian month-names sometimes substituted for the Babylonian names (Stern, 2012:238). The A.G. calendar uses the same 19 year cycle of intercalations as the Babylonian calendar. There are two start dates. The Macedonian reckoning used by court officials in the Seleucid Empire and native Greek speakers started in the Autumn of 312 BCE with the start date eventually getting fixed to 1 Oct. 312 BCE. The Babylonian reckoning used by most Semitic speaking populations has a start date of 1 Nisan in 311 BCE. Ambraseys (2009) equates this to 1 April, Guidoboni et al (1994) equate this with 2 April, and others equate it to 3 April. A version of the A.G. calendar was used by the Christian Syriac authors such as Pseudo-Dionysius of Tell Mahre and Chronicon Ad Annum 1234. Syriac writing authors would have likely used the Macedonian reckoning as this was the standard usage among these authors for the Seleucid era (Sebastian Brock, personal communication, 2021 – see also Stern, 2012:236). In the Anno Graecorum calendar system, the day starts at sundown (Sebastian Brock, personal communication, 2022).

Macedonian Months and Julian equivalent dates
Sources: Meimaris and Kritikakou (2005) and Theodossiou et al (1997)
Macedonian Month Julian Equivalent Duration (days)
Xanthikos 22 March - 20 April 29
Artemisios 21 April - 20 May 30
Daisios 21 May - 19 June 29
Panemos 20 June - 19 July 30
Loos 20 July - 18 Aug. 29
Gorpiaios 19 Aug. - 17 Sept. 30
Hyperberetaios 18 Sept. - 17 Oct. 29
Dios 18 Oct. - 16 Nov. 30
Apellaios 17 Nov. - 16 Dec. 29
Audynaios 17 Dec. - 15 Jan. 30
Peritios 16 Jan. 14 Febr. 29
Dystros 15 Febr. - 16 March 30
Epagomenai 17 March - 21 March 5

Syriac Calendar

Names of months and days in the Syriac Calendar

Automating the Liturgical Calendar of the Syriac Orthodox Church



The Coptic Calendar is also known as the Alexandrian Calendar. The Coptic Calendar is coordinated with the Julian Calendar and, since the 4th century CE, used a starting year (Year 1) from 29 August 284 CE to 28 August 285 CE. A year consists of 13 months where the first 12 months have 30 days each followed an epagomenal month which has 5 days during normal years and 6 days during leap years. This version of the Coptic calendar is frequently called the Era of Martyrs and is frequently abbreviated as A.M. (Anno Martyrum). Coptic Leap Years are coordinated with Julian leap years however the coptic leap day is added on the last day of the coptic year rather than on 29 February. If a Coptic year will encompass a Julian Leap year (i.e. a year where there will be a February 29), the coptic year will start on 30 August instead of 29 August as 29 August in the previous Coptic year will be a leap day. In years such as this, the coptic day will be a day ahead of the Julian Calendar until 29 February. Thus, for example while 21 Tuba normally corresponds to 16 January, in a Julian Leap Year it will correspond to 17 January. The Coptic day begins at sunrise in the civil calendar and sunset in the liturgical version (Coptic Encyclopedia).

The Coptic Calendar - Claremont Coptic Encyclopedia

The Coptic Calendar - timeanddate.com

The Coptic Calendar by Bishoy Dawood

Converts from Julian to Coptic and other calendars

Chaine, M. (1925). La chronologie des temps chrétiens de l'Égypte et de l'Éthiopie; historique et exposé du calendrier et du comput de l'Égypte et de l'Éthiopie depuis les débuts de l'ère chrétienne à nous jours, accompagnés de tables donnant pour chaque année, avec les caractéristiques astronomiques du comput alexandrin, les années correspondantes des principales ères orientales, suivis d'une concordance des années juliennes, grégoriennes, coptes et éthiopiennes avec les années musulmanes, et de plusieurs appendices, pour servir à la chronologie. Paris, P. Geuthner.



A.H. – Anno Hegirae is also known as the Muslim Calendar or the Islamic lunar calendar. The start date is the Hijra - when on Friday 16 July 622 CE, Mohammed and his followers migrated from Mecca to Medina. The calendar consists of 12 alternating months of 30 and 29 days. Although the original calendar determined the start of each month based on astronomical observation of the first visible crescent after a new moon, a fixed tabular calendar was developed in the 8th century CE. In the tabular calendar, a day is added to the final (12th) month during leap years making it 30 days long instead of 29. Leap days are added every 2-3 years in a 30 year cycle which is subject to local variation. The most common distribution is on the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th year of each 30-year cycle (timeanddate.com). The Islamic day begins at sundown.

The Islamic Calendar - timeanddate.com



The Hebrew Calendar is also known as the Jewish Calendar or HaLuah HaIvri (הַלּוּחַ הָעִבְרִי) in Hebrew. The Hebrew Calendar is a lunisolar calendar influenced by the Ancient Babylonian Calendar which has undergone revisions over time. Initially, this calendar was based on sightings of the first crescent after the new moon. After the destruction of the 2nd temple in 70 CE and throughout the diaspora, the calendar was subject to local variations. By the 4th century CE, a calendar had emerged which was increasingly based on predicted lunar cycles. Sometime before the 8th century, a fixed 19 year Metonic cycle of intercalations similar to the Babylonian cycle was adopted and by the early 10th century, the rabbinic calendar had become like the fixed and predictable calendar that is used today. (Stern, 2012:334-335), The structure of the Hebrew Calendar is one of 12 months with an additional intercalary month added in years 3, 6, 8, 11, 14, 17, and 19 of the Metonic cycle along with a complicated set of rules (Reingold and Dershowitz, 2018:Section 8.1). The modern Hebrew Calendar is also characterized by a change in the start date of the calendar from the destruction of the second Temple in 70 CE to the start of “creation” like the Anno Mundi Calendar of the Byzantines. In the Hebrew Calendar, the day begins at sundown.

Modern Hebrew Calendar Rules from Stern (2001:191-193)

4.4.1 The Present-Day Rabbinic Calendar: An Outline

  1. The conjunction (molad) is calculated on the basis of two values
    1. the mean lunation (duration of the lunar month) of 29 days, 12 hours, and 793 parts (there are 1080 parts to an hour).
    2. molad of Tishre year 1 (of the era of creation, i.e. the first Tishre in ‘history’), which is given as 2nd day (Monday), 5 hours (of the 24-hour period beginning in the evening), 204 parts, or in its Hebrew acronym: (BaHaRaD). This corresponds to Sunday, 6 October 3761 BCE at 23 hours, 11 minutes, and 20 seconds (assuming the day begins at 18 hours). The molad of Tishre year 1 functions as an epoch (reference point). Any subsequent molad can be worked out by adding the right number of lunations to this epoch. As an alternative to BaHaRaD, the molad of the following Tishre (year 2) can also be used. This molad is 6th day (Friday), 14 hours, no parts (acronym: WeYaD).The fact that this epoch is a round figure (with no parts of the hour) suggests that this was the original epoch to have been in use.
  2. The month begins, apriori, on the day of the molad. Sometimes it is postponed by one or more days, because of the rules that follow (iii–iv), which are hence known as ‘postponement’ rules.
  3. Rosh ha-Shanah, 1 Tishre, cannot occur on Sunday, Wednesday, on Friday. This rule is known by its Hebrew mnemonic: (lo ADURosh). If the molad of Tishre occurs on any of these days, the 1st of the month must be postponed.
  4. If the molad of Tishre occurs on or after the 18th hour (i.e. midday), the 1st of the month must be postponed. (footnote: If the following day is either Sunday, Wednesday, or Friday, Rosh ha-Shanah must be postponed till the day after, hence a postponement of two days.) This is known as molad zaqen (‘late conjunction’).
  5. The calendar consists of a fixed alternation of 29 and 30 day months: there are always 30 days in Nisan, 29 days in Iyyar, etc. Only the months of Marḥeshwan and Kislew are subject to variation: they can be ‘regular’ (i. e. 29–30), ‘full’ (i.e. 30–30), or ‘defective’ (i.e. 29–29) . This variation makes it possible for rules (iii) and (iv) to be observed, i.e. for the subsequent Rosh ha-Shanah(s) (sometimes more than one year ahead) not to occur on the wrong days. This variation also makes it possible to compensate for the discrepancy between the mean lunation under rule (i)(a) and the average month length of 29½ days resulting from a pure alternation of 29- and 30-day months.
  6. The intercalation is based on a fixed 19-year cycle, which starts at year 1 (from the creation) and within which the following seven years are intercalated: 3, 6, 8, 11, 14, 17, 19. Intercalation consists of an additional 30-day month, which is inserted before Adar and called ‘first Adar’
From the late Geonic period until the present day, a number of tables and algorithms have been designed and formulated on the basis of these fundamental principles, so as to facilitate the calendar calculation and remove unnecessary complications. Among the earliest of these algorithms were the cycle attributed to R. Naḥshon (gaon of Sura, 871–9), and the table known as (‘four gates’ or ‘four parts’ table) which was already in existence and apparently widespread in R. Saadya's time. The ‘four parts table’ represents the earliest formulation of the normative rabbinic calendar, with which it corresponds down to the finest detail. All it requires is knowledge of the molad and of the cycle of intercalations; on this basis, calendar dates can be worked out with the greatest of ease.

Hebrew Calendar Calculator

The Hebrew Calendar - wikipedia

Stern, S. (2001). Calendar and Community: A History of the Jewish Calendar, 2nd Century BCE to 10th Century CE.. S

Seasonal Drift of the Hebrew Calendar

Era of Province Arabia


The Bostran era (also called the era of Bostra, the Arabian era or provincial era) was a calendar era (year numbering) with an epoch (start date) corresponding to 22 March 106 AD. It was the official era of the Roman province of Arabia Petraea, introduced to replace dating by regnal years after the Roman annexation of the Nabataean Kingdom. It is named after the city of Bostra, which became the headquarters of the Sixth Legion stationed in the province.


Parker and Dubbstein (1956) Babylonian chronology 626 B.C.-A.D. 75

Parker and Dubbstein (1956) Babylonian chronology 626 B.C.-A.D. 75 - another online copy

Babylonian Calendar Converter (626 BCE to 75 CE)

Babylonian Calendar - wikipedia


Ho Peng, Y. (1962). "Ancient and mediaeval observations of comets and novae in Chinese sources." Vistas in Astronomy 5: 127-225.. HPY

Pingré, A. G. (1784). Cométographie: ou, Traité historique et théorique des comètes, Imprimerie royale.

BIOT, É. C. (1846). Catalogue des comètes observées en Chine depuis l'an 1230 jusqu'à l'an 1640 de notre ère, faisant suite au catalogue de Ma-touan-lin ... et extrait du supplément du Wen-hian-thoung-khao, et de la grande Collection des vingt-cinq historiens de la Chine ... Extrait des “Additions à la Connaissance des Temps” pour 1846.

Biot, E. (1846). Catalogue: Des étoiles extraordinaires obsenvées en Chine depuis les temps anciens juqu'à l'an 1203 de notre ère.

Biot, E. (1846). Recherches faites dans les grandes collections des historiens de la Chine

Williams, J. (1871). Observations of comets, from B.C. 611 to A.D. 1640 : Extracted from the Chinese annals. Translated, with introductory remarks, and an appendix, comprising the tables necessary for reducing Chinese time to European reckoning and a Chinese celestial atlas. London

Chambers, Georges F., 1909, The Story of the Cornets, Clarendon Press, Oxford, 1909.

Grumel, V. (1958). La chronologie, Presses Universitaires de France PAGE 458.. G GE


Five Millenium Solar Eclipse Search Engine (NASA)

NASA Eclipse website - Solar Eclipse Page

Five millenium Catalog of Lunar Eclipses (NASA)

NASA Eclipse website - Lunar Eclipse Page

Grumel, V. (1958). La chronologie, Presses Universitaires de France PAGE 469... G GE