Modern calendar era
Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the original Anno Domini (AD) and Before Christ (BC) notations used for the same calendar era. The two notation systems are numerically equivalent: "2025 CE" and "AD 2025" each describe the current year; "400 BCE" and "400 BC" are the same year.
The expression can be traced back to 1615, when it first appears in a book by Johannes Kepler as the (), and to 1635 in English as "Vulgar Era". The term "Common Era" can be found in English as early as 1708, and became more widely used in the mid-19th century by Jewish religious scholars. Since the late 20th century, BCE and CE have become popular in academic and scientific publications on the grounds that BCE and CE are religiously neutral terms. They have been promoted as more sensitive to non-Christians by not referring to Jesus, the central figure of Christianity, especially via the religious terms "Christ" and ("Lord") used by the other abbreviations. Nevertheless, its epoch remains the same as that used for the Anno Domini era.
History.
Origins.
The idea of numbering years beginning from the date that he believed to be the date of birth of Jesus, was conceived around the year 525 by the Christian monk Dionysius Exiguus. He did this to replace the then dominant Era of Martyrs system, because he did not wish to continue the memory of a tyrant who persecuted Christians. He numbered years from an initial reference date ("epoch"), an event he referred to as the Incarnation of Jesus. Dionysius labeled the column of the table in which he introduced the new era as "Anni Domini Nostri Jesu Christi" (Of the year of our Lord Jesus Christ].
This way of numbering years became more widespread in Europe with its use by Bede in England in 731. Bede also introduced the practice of dating years before what he supposed was the year of birth of Jesus, without a year zero. In 1422, Portugal became the last Western European country to switch to the system begun by Dionysius.
Vulgar Era.
The term "Common Era" is traced back in English to its appearance as "Vulgar Era" to distinguish years of the Anno Domini era, which was in popular use, from dates of the regnal year (the year of the reign of a sovereign) typically used in national law.
The first use of the Latin term may be that in a 1615 book by Johannes Kepler. Kepler uses it again, as , in a 1616 table of ephemerides, and again, as , in 1617. A 1635 English edition of that book has the title page in English that may be the earliest-found use of "Vulgar Era" in English. A 1701 book edited by John Le Clerc includes the phrase "Before Christ according to the Vulgar Æra,6".
The Merriam Webster Dictionary gives 1716 as the date of first use of the term "vulgar era" (which it defines as Christian era). 
The first published use of "Christian Era" may be the Latin phrase on the title page of a 1584 theology book, . In 1649, the Latin phrase appeared in the title of an English almanac. A 1652 ephemeris may be the first instance found so far of the English use of "Christian Era".
The English phrase "Common Era" appears at least as early as 1708, 
and in a 1715 book on astronomy it is used interchangeably with "Christian Era" and "Vulgar Era". A 1759 history book uses "common æra" in a generic sense, to refer to "the common era of the Jews". The first use of the phrase "before the common era" may be that in a 1770 work that also uses "common era" and "vulgar era" as synonyms, in a translation of a book originally written in German. The 1797 edition of the Encyclopædia Britannica uses the terms "vulgar era" and "common era" synonymously. 
In 1835, in his book "Living Oracles", Alexander Campbell, wrote: "The vulgar Era, or Anno Domini; the fourth year of Jesus Christ, the first of which was but eight days", 
and also refers to the "common era" as a synonym for "vulgar era" with "the fact that our Lord was born on the 4th year before the vulgar era, called Anno Domini, thus making (for example) the 42d year from his birth to correspond with the 38th of the common era". The "Catholic Encyclopedia" (1909) in at least one article reports all three terms (Christian, Vulgar, Common Era) being commonly understood by the early 20th century.
The phrase "common era", in lower case, also appeared in the 19th century in a "generic" sense, not necessarily to refer to the Christian Era, but to any system of dates in common use throughout a civilization. Thus, "the common era of the Jews", "the common era of the Mahometans", "common era of the world", "the common era of the foundation of Rome". 
When it did refer to the Christian Era, it was sometimes qualified, e.g., "common era of the Incarnation", "common era of the Nativity", or "common era of the birth of Christ".
An adapted translation of "Common Era" into Latin as was adopted in the 20th century by some followers of Aleister Crowley, and thus the abbreviation "e.v." or "EV" may sometimes be seen as a replacement for AD.
History of the use of the CE/BCE abbreviation.
Although Jews have their own Hebrew calendar, they often use the Gregorian calendar without the AD prefix. As early as 1825, the abbreviation VE (for Vulgar Era) was in use among Jews to denote years in the Western calendar. As of 2005[ [update]], Common Era notation has also been in use for Hebrew lessons for more than a century. Jews have also used the term Current Era.
Contemporary usage.
Some academics in the fields of theology, education, archaeology and history have adopted CE and BCE notation despite some disagreement. A study conducted in 2014 found that the BCE/CE notation is not growing at the expense of BC and AD notation in the scholarly literature, and that both notations are used in a relatively stable fashion. 
Australia.
In 2011, media reports suggested that the BC/AD notation in Australian school textbooks would be replaced by BCE/CE notation. The change drew opposition from some politicians and church leaders. Weeks after the story broke, the Australian Curriculum, Assessment and Reporting Authority denied the rumours and stated that the BC/AD notation would remain, with CE and BCE as an optional suggested learning activity.
Canada.
In 2013, the Canadian Museum of Civilization (now the Canadian Museum of History) in Gatineau (opposite Ottawa), which had previously switched to BCE/CE, decided to change back to BC/AD in material intended for the public while retaining BCE/CE in academic content.
Nepal.
The notation is in particularly common use in Nepal in order to disambiguate dates from the local calendar, Bikram or Vikram Sambat. Disambiguation is needed because the era of the local calendar is quite close to the Common Era.
United Kingdom.
In 2002, an advisory panel for the religious education syllabus for England and Wales recommended introducing BCE/CE dates to schools, and by 2018 some local education authorities were using them. 
In 2018, the National Trust said it would continue to use BC/AD as its house style. English Heritage explains its era policy thus: "It might seem strange to use a Christian calendar system when referring to British prehistory, but the BC/AD labels are widely used and understood." Some parts of the BBC use BCE/CE, but some presenters have said they will not. As of October 2019, the BBC News style guide has entries for AD and BC, but not for CE or BCE. The style guide for "The Guardian" says, under the entry for CE/BCE: "some people prefer CE (common era, current era, or Christian era) and BCE (before common era, etc.) to AD and BC, which, however, remain our style".
United States.
In the United States, the use of the BCE/CE notation in textbooks was reported in 2005 to be growing. Some publications have transitioned to using it exclusively. For example, the 2007 World Almanac was the first edition to switch to BCE/CE, ending a period of 138 years in which the traditional BC/AD dating notation was used. BCE/CE is used by the College Board in its history tests, and by the Norton Anthology of English Literature. Others have taken a different approach. The US-based History Channel uses BCE/CE notation in articles on non-Christian religious topics such as Jerusalem and Judaism. The 2006 style guide for the Episcopal Diocese "Maryland Church News" says that BCE and CE should be used.
In June 2006, in the United States, the Kentucky State School Board reversed its decision to use BCE and CE in the state's new Program of Studies, leaving education of students about these concepts a matter of local discretion.
Rationales.
Support.
The use of CE in Jewish scholarship was historically motivated by the desire to avoid the implicit "Our Lord" in the abbreviation "AD". Although other aspects of dating systems are based in Christian origins, AD is a direct reference to Jesus as Lord. Proponents of the Common Era notation assert that the use of BCE/CE shows sensitivity to those who use the same year numbering system as the one that originated with and is currently used by Christians, but who are not themselves Christian. Former United Nations Secretary-General Kofi Annan has argued:
 ;templatestyles src="Template:Blockquote/styles.css" / ;[T]he Christian calendar no longer belongs exclusively to Christians. People of all faiths have taken to using it simply as a matter of convenience. There is so much interaction between people of different faiths and cultures – different civilizations, if you like – that some shared way of reckoning time is a necessity. And so the Christian Era has become the Common Era.
Adena K. Berkowitz, in her application to argue before the United States Supreme Court, opted to use BCE and CE because, "Given the multicultural society that we live in, the traditional Jewish designations – B.C.E. and C.E. – cast a wider net of inclusion." In the World History Encyclopedia, Joshua J. Mark wrote "Non-Christian scholars, especially, embraced [CE and BCE] because they could now communicate more easily with the Christian community. Jewish, Islamic, Hindu and Buddhist scholars could retain their [own] calendar but refer to events using the Gregorian Calendar as BCE and CE without compromising their own beliefs about the divinity of Jesus of Nazareth." In "History Today", Michael Ostling wrote: "BC/AD Dating: In the year of whose Lord? The continuing use of AD and BC is not only factually wrong but also offensive to many who are not Christians."
Opposition.
Critics note the fact that there is no difference in the epoch of the two systems—chosen to be close to the date of birth of Jesus. Since the year numbers are the same, BCE and CE dates should be equally offensive to other religions as BC and AD. Roman Catholic priest and writer on interfaith issues Raimon Panikkar argued that the BCE/CE usage is the less inclusive option since they are still using the Christian calendar numbers and forcing it on other nations. In 1993, the English-language expert Kenneth G. Wilson speculated a slippery slope scenario in his style guide that, "if we do end by casting aside the AD/BC convention, almost certainly some will argue that we ought to cast aside as well the conventional numbering system [that is, the method of numbering years] itself, given its Christian basis."
Some Christians are offended by the removal of the reference to Jesus, including the Southern Baptist Convention.
Conventions in style guides.
The abbreviation BCE, just as with BC, always follows the year number. Unlike AD, which still often precedes the year number, CE always follows the year number (if context requires that it be written at all). Thus, the current year is written as 2025 in both notations (or, if further clarity is needed, as 2025 CE, or as AD 2025), and the year that Socrates died is represented as 399 BCE (the same year that is represented by 399 BC in the BC/AD notation). The abbreviations are sometimes written with small capital letters, or with periods (e.g., "B.C.E." or "C.E."). The US-based Society of Biblical Literature style guide for academic texts on religion