BC means Before Christ, AD means Anno Domini (“in the year of our Lord”), BCE means Before Common Era, and CE means Common Era. BC and BCE refer to the same years, as do AD and CE. The BC/AD system developed in Christian Europe and was based on a chronology created by the sixth-century monk Dionysius Exiguus.
Most of us rarely think about the numbers attached to historical dates. We simply accept that Julius Caesar was assassinated in 44 BC, Jerusalem was destroyed by the Romans in AD 70, and we are living more than two thousand years after the traditional date assigned to the birth of Jesus Christ.
But people living in the ancient world did not say that an event occurred in “300 BC.” They did not know they were living “before Christ.” Nor did the earliest Christians routinely describe themselves as living in AD 100 or AD 200.
Those designations were created centuries later.
Understanding BC, AD, BCE, and CE therefore requires more than defining four abbreviations. It takes us into the history of calendars themselves—and into the surprisingly complicated question of how human beings decided to number the years.
What Do BC, AD, BCE, and CE Mean?
BC means Before Christ.
AD is an abbreviation of the Latin Anno Domini, meaning “in the year of the Lord.” Contrary to a common misconception, AD does not mean “After Death.”
BCE means Before Common Era.
CE means Common Era.
The important point is that these are two sets of names for exactly the same numbered years:
- 500 BC = 500 BCE
- AD 70 = 70 CE
- AD 2026 = 2026 CE
Changing from BC/AD to BCE/CE does not change the calendar or move the dividing point. It changes only the terminology used to describe the eras.
But how did this particular dividing point become so important?
Before BC and AD
Ancient civilizations developed many different ways of keeping track of time.
Calendars originally served extremely practical purposes. Agricultural societies needed to know when seasons were changing. Governments needed to establish tax periods and official dates. Religious communities needed calendars for festivals and holy days.
Different civilizations solved the problem differently.
The ancient Egyptians developed calendars associated with the solar year and the flooding of the Nile. Jewish timekeeping developed around a lunisolar calendar and religious festivals. Greeks sometimes identified years in relation to Olympiads or officials. Romans frequently identified years by the consuls serving during that year.
Another Roman method counted years from the traditional founding of Rome, later expressed as Ab urbe condita—“from the founding of the city.”
In other words, there was no universally accepted “Year 1.”
A calendar needs a reference point before its years can be numbered, and different cultures chose different reference points.
Julius Caesar and the Julian Calendar
One of the most important developments came from Julius Caesar.
The Roman calendar had accumulated serious problems in keeping the calendar aligned with the seasons. Caesar therefore instituted a major reform, traditionally dated to 46 BC and implemented beginning in 45 BC.
The resulting Julian calendar used a year of approximately 365¼ days. Ordinarily a year contained 365 days, with an additional day inserted every fourth year.
The system was remarkably successful. Variations of the Julian calendar remained dominant throughout much of Europe for more than 1,600 years.
But there is an important distinction:
Julius Caesar helped establish the calendar structure. He did not establish the BC/AD numbering system.
That came centuries later.
Christians Still Needed a Way to Number the Years
Christianity arose within the Jewish and Roman worlds, so early Christians inherited existing methods of dating events.
They did not immediately create a calendar beginning with Jesus.
Christians might identify a year according to a Roman emperor’s reign or other chronological systems. One system used in the Christian world counted years beginning with the reign of Emperor Diocletian.
That created an uncomfortable situation because Diocletian was remembered for a severe persecution of Christians.
Then, in the sixth century, a monk named Dionysius Exiguus helped change the way Western civilization would eventually number history.
Dionysius Exiguus and Anno Domini
Around AD 525, Dionysius was working on calculations related to the date of Easter.
Rather than continuing to number years according to the era associated with Diocletian, Dionysius established a system centered upon Jesus Christ.
He called the years Anno Domini nostri Jesu Christi—the “year of our Lord Jesus Christ.”
This is the origin of AD — Anno Domini.
This also explains something about the proper use of the abbreviation.
Traditionally we write:
AD 325
rather than:
325 AD
because the expression means:
“In the year of our Lord 325.”
BC works differently and normally follows the number:
325 BC
Modern CE and BCE generally follow the number:
325 CE
325 BCE.
Did Dionysius Get the Birth of Jesus Right?
Probably not exactly.
Dionysius intended his chronology to be based upon the coming of Christ, but historians generally believe Jesus was born several years earlier than the date implied by the system—often estimated somewhere around 6–4 BC.
That produces the seemingly strange statement:
Jesus was probably born “before Christ.”
There is no actual contradiction. BC is simply the name subsequently attached to years preceding the chronological boundary Dionysius established. If his calculation of Jesus’ birth was off by several years, the numbering system can remain intact even though its original historical estimate was imperfect.
The system had become a convention.
And conventions do not have to be recalculated whenever historians revise the date of an ancient event.
Where Did “BC” Come From?
Dionysius primarily developed a system for numbering years forward from the Christian era. The systematic use of years before Christ developed later.
An important figure in popularizing Christian chronology was the English monk and historian Bede, who lived in the seventh and eighth centuries.
Bede used a form of dating corresponding to years “before the incarnation of the Lord” in his historical writings. His influential Ecclesiastical History of the English People, completed in the eighth century, helped establish Christ-centered dating in Western historical writing.
Eventually the familiar English designation **BC—Before Christ—**became standard.
History could now be visualized as running in two directions around the beginning of the Christian era:
500 BC → 100 BC → 1 BC → AD 1 → AD 100 → AD 500
And that introduces one of the strangest features of our calendar.
There Is No Year Zero
In the traditional BC/AD historical system, the sequence goes:
3 BC → 2 BC → 1 BC → AD 1 → AD 2 → AD 3
There is no year zero.
The same applies when BCE and CE are used:
3 BCE → 2 BCE → 1 BCE → 1 CE → 2 CE → 3 CE
That matters when calculating intervals that cross the BC/AD boundary.
It also explains why, technically, the first century consisted of years 1 through 100, the second century of 101 through 200, and so forth.
Astronomers and some scientific systems can use a year zero for mathematical convenience, but that is different from conventional historical BC/AD chronology.
The Gregorian Calendar
The Julian calendar was excellent for its time, but it contained a small mathematical error.
Its average year was slightly longer than the actual solar year. A discrepancy of only minutes per year seems insignificant, but over many centuries those minutes accumulated into days.
This created particular problems for calculating the date of Easter.
In 1582, Pope Gregory XIII instituted a calendar reform. The new system modified the leap-year rules and corrected the accumulated calendar drift.
The result became known as the Gregorian calendar.
The Gregorian calendar was not adopted everywhere simultaneously. Catholic countries generally adopted it first, while Protestant and Orthodox countries often followed much later.
Nevertheless, it eventually became the dominant civil calendar internationally.
This gives us another distinction that is easy to miss:
The calendar and the era designation are not exactly the same thing.
The Gregorian calendar determines such things as months, days and leap years.
BC/AD or BCE/CE tells us how the years are numbered and labeled.
Where Did BCE and CE Come From?
Some people assume BCE and CE were invented very recently to remove Christianity from the calendar.
The history is considerably more complicated.
Expressions equivalent to “Common Era” have existed for centuries. Merriam-Webster traces English use of “Common Era” to 1651, while forms of the terminology became increasingly established in subsequent centuries. English examples of CE/BCE-style terminology appear by the early eighteenth century.
Historically, expressions such as Christian Era, Common Era, and even Vulgar Era were used. In older English, “vulgar” could simply mean ordinary or commonly used rather than crude or offensive.
Over time, CE came to mean Common Era, while BCE became Before Common Era.
Their use became especially attractive in academic, archaeological and interreligious contexts because scholars from many religious traditions could use the same chronological system without explicitly describing Jesus as “Christ” or “Lord.”
Did BCE and CE Remove Jesus from the Calendar?
They removed the explicitly Christian terminology, but they did not change the chronological dividing point.
This is an important distinction.
Suppose we write:
Jerusalem was destroyed in AD 70.
Then change it to:
Jerusalem was destroyed in 70 CE.
Nothing about the date has changed.
Likewise:
Alexander the Great died in 323 BC
and
Alexander the Great died in 323 BCE
refer to exactly the same year.
CE/BCE simply relabel the existing chronology.
There is therefore an interesting historical irony. Even when the explicitly Christian words are removed, the conventional numbering system still traces its historical development to a sixth-century Christian monk attempting to organize chronology around Jesus Christ.
Why Do Scholars Often Use BCE and CE?
Modern universities, museums, archaeologists, historians and academic publishers frequently prefer BCE and CE because the terminology can be used regardless of a writer’s religious beliefs.
A Jewish historian discussing the Roman Empire, for example, does not have to describe a year as “in the year of our Lord.” A secular archaeologist can use the same chronology as a Christian theologian without making a theological statement.
That is largely why BCE and CE have become common in academic writing. Some style authorities explicitly prefer them, although BC and AD remain widely understood and accepted.
The choice therefore does not require us to imagine two competing calendars.
There aren’t two.
There are two principal ways of labeling the same chronological era.
Why Does the Whole World Use a Christian-Derived Calendar?
The answer is primarily historical rather than theological.
European civilization used the Christian dating system for centuries. European exploration, colonization, commerce, diplomacy and eventually global political and economic systems spread European methods of dating.
The Gregorian calendar gradually became useful as an international civil standard.
A Muslim, Jew, Hindu or Buddhist may therefore use the Gregorian year for business and government while simultaneously observing a religious calendar belonging to his or her own tradition.
Judaism still has the Hebrew calendar.
Islam has the Islamic Hijri calendar.
Other civilizations and religious traditions maintain their own systems as well.
So when people throughout the world write a year such as 2026, they are not necessarily making a Christian confession. They are participating in an internationally standardized chronological convention whose historical development happened to occur largely within Christian Europe.
BC/AD or BCE/CE: Which Should Christians Use?
There is no need to turn the terminology into a theological test.
BC and AD preserve the explicitly Christian history of the system. **Anno Domini—“in the year of the Lord”—**is a reminder that Western chronology was deliberately organized around Jesus Christ.
For Christian historical and theological writing, there is therefore a reasonable argument for retaining BC and AD.
BCE and CE, however, do not constitute a different chronology and using them does not inherently deny Christ. They are conventional labels widely used in modern historical and academic scholarship.
A Christian writer may therefore choose terminology according to audience and context.
What matters most is understanding what the terminology actually means.
A Calendar Tells a Story
Calendars appear to be nothing more than numbers.
They aren’t.
Every calendar reflects decisions about what should be remembered, where history begins, how seasons should be measured and which events are important enough to organize human life around them.
Ancient Romans could date events according to consuls or the traditional founding of Rome. Jewish communities organized time around their own sacred history and festivals. Christians eventually developed a chronology centered upon the coming of Christ. Modern international society inherited and standardized much of that system.
That long development eventually produced the terminology we encounter today:
BC — Before Christ
AD — Anno Domini, “in the year of the Lord”
BCE — Before Common Era
CE — Common Era
The labels have changed, but the numbers have not.
And beneath those familiar numbers lies nearly two thousand years of astronomy, religion, politics, scholarship and human attempts to answer a deceptively simple question:
What year is it?