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AD vs. BC


AD or A.D. stands for Anno Domini and is a label for numbering years after Christ was born. BC or B.C. means Before Christ. The year Christ was born is considered AD 1 and the year before that is labeled 1 BC. Historians use a nomenclature with less religious connotation: namely CE/BCE where CE means «Common Era» and BCE stands for Before Common Era. Although the labels used are different, BC and BCE are the same and so are AD and CE. This system of numbering years was invented by Dionysius Exiguus in AD 525 and is used in the Julian and Gregorian calendars.

Comparison chart

AD versus BC comparison chart

Stands for Anno Domini (Latin for Year of our Lord) Before Christ
Also known as CE (Common Era) BCE (Before Common Era)
Writing style AD 2013 45 BC

This special £5 coin was made in 1999, before the turn of the century (from the 20th to 21st centuries / AD 1999 - 2000). On one side it marks GMT (Greenwich Mean Time) with the line going through Greenwich.

This special £5 coin was made in 1999, before the turn of the century (from the 20th to 21st centuries / AD 1999 — 2000). On one side it marks GMT (Greenwich Mean Time) with the line going through Greenwich.

What is A.D.?

AD stands for Anno Domini, which is Latin for «Year of our Lord,» and is used to number years in the Julian and Gregorian calendars. AD denotes the calendar era after the birth of Jesus Christ. The traditionally accepted year of Christ’s birth is labeled AD 1 and the year before is 1 BC. This calendaring system was devised in AD 525, but was not widely used until after AD 800. An alternative for AD is CE, which stands for Common Era, Christian Era or Current Era.

What is B.C.?

B.C. stands for Before Christ, and it means the number of years before the time of Jesus Christ. The use of B.C. is believed to originate with Bede in the 8th century (AD). The Latin version is «ante vero incarnationis dominicae tempus» («the time before the Lord’s true incarnation»), equivalent to the English term «before Christ» which was used by Dionysius Exiguus.

Numbering scheme

In the Common Era (CE or AD), the years are numbered in chronological order i.e. the year AD 401 followed the year AD 400. However, in the BC or BCE era, the years are numbered in the reverse order i.e. the year 300 BC followed the year 301 BC.

Did you know?

  • The Hebrew calendar considers the year 3760 BC as year 1.
  • In the Islamic calendar, the year 622 AD is year 1 because Prophet Mohammed embarked on a holy journey in that year.
  • Buddha died over 400 years before Christ was born.
  • While AD 1 is when Christ was believed to have been born when this system was invented, historians now believe that Christ was actually born between 7 BC and 4 BC.


  • wikipedia:Anno Domini
  • wikipedia:Common Era

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Что такое ad в впн

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BC, AD, BP, BCE, CE, ka, cal, circa: What’s the difference?

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  • Jui Shirvalkar
  • April 5, 2021

Whether you’re studying History or Literature, confusing dating notations such as AD 2000 or 300 CE are always going to be there. Perhaps it was easier when only the BC-AD calendar marking system was used. These other acronyms like BCE, CE, BP, etc. started slipping in the books slowly and messed up our year counting system. But, you know, even though the letters are different, the new system is not that difficult to understand.

Notation Full-form Short Description
BC Before Christ before the birth of Jesus Christ
AD Anno Domini A Latin phrase that means ‘in the year of our lord’ (refers to Jesus Christ – in the year that our Lord Christ was born)
BP Before Present before the year 1950
BCE Before Common Era equivalent to BC
CE Common Era equivalent to AD
ka or kyr or KY kilo annum a thousand years
c. or ca. Circa The Latin word for around or approximately
cal Calibrated

BC, AD, BP, BCE, CE, ka, cal: Meaning in brief

What we are studying here – Literature, Literary Movements, Philosophy, History, Linguistics – all these subjects use these notations. So, it was best to clear our concepts before moving on to them.

Are you ready? Let’s dig in!

Image Thumbnail for BC, AD, BP, BCE, CE, KA, CAL, CIRCA: WHAT’S THE DIFFERENCE? A Good Library agoodlibrary.com agoodlibrary

All numbers on the right side of (or those that come before) “0” are positive and those on the left side of (or those who come after) “0” are marked negative. -200 is greater than -300 whereas 300 is greater than 200.

Similarly, we are using Christ’s birth as the “0” mark on the number line. So, BC 4 happened 2 years earlier than BC 2.

BC, AD, BP, BCE, CE, KA, CAL, CIRCA: WHAT’S THE DIFFERENCE? A Good Library agoodlibrary.com agoodlibrary

That means we move from

Christ’s birth to

But the main difference between the number line and the year mapping is:

BC, AD, BP, BCE, CE, KA, CAL, CIRCA: WHAT’S THE DIFFERENCE? A Good Library agoodlibrary.com agoodlibrary

Number Line Year Mapping
There is a neutral point “0”. THERE IS NO YEAR “0”.
The specific point is marked as “1” & not the entire space between 0 and 1. The entire space between 0 (the theoretical birth of Christ) and the next point is marked 1.
There are infinite points between 0 and 1 (or any two consecutive integers) There are exactly 365 (or 366) days between 2 consecutive years.
The difference between -2 and +3 is 5. The difference between 2 BC and 3 AD is 4 years. There are 4 laps as we don’t have a Year Zero. Look at the image below.

BC, AD, BP, BCE, CE, KA, CAL, CIRCA: WHAT’S THE DIFFERENCE? A Good Library agoodlibrary.com agoodlibrary

There are exactly 4 years between the date August 15, 03 BC and August 15, 02 AD.

What is cal? What are Calibrated Dates?

After the scientists started using Carbon Dating to find out the dates of an item, they realized that it gave them dates that didn’t match with the calendar years. The method Carbon Dating a.k.a. Radiocarbon Dating a.k.a Carbon-14 Dating helps us find out the age of an object from the radiocarbon content in it. Let’s not get into the science part of it. Anyway, the amount of carbon in the atmosphere has fluctuated a lot over the years. So, the scientists saw that these carbon fluctuations altered the dates deduced using this method.

To find out the precise time, scientists then took the help of different methods such as the Tree-Ring method (dendrochronology), examination of volcanic eruptions, ice cores, sedimentary layering, cave deposits, etc. These methods used in unison with Carbon Dating helped them calibrate the dates.

The notation of whether the date is calibrated or not is as follows:

Abbreviation (Usually used) Calibration Example
Upper case abbreviation ‘BC’ And/OR The word ‘cal’ Calibrated Uncalibrated date: 3000 bc
calibrated to
3347 BC or 3347 cal BC
Lower case abbreviation ‘bc’(But, sometimes, Upper Case ‘BC’ is used too.) Uncalibrated 3000 bc

What is BP?

The acronym ‘BP’ or ‘bp’ stands for ‘Before Present’ ~ ‘years before present’.

IMPORTANT: – The date in ‘Before Present’ is not really ‘the Present’. The ‘present’ in ‘BP’ is January 1, 1950.

(Since Carbon Dating was discovered in the 1940s. Also, the present time is never constant.)

Is BP the same as BC?

In the calendar marking system, BP is not the same as BC. BP is ‘Before Present’ while BC is ‘Before Christ’. According to the standard practices, the present is set to 1950 AD. Therefore, there is a difference of around 1950 years in a BC and BP year.

How do you convert BP to BC/AD or BCE/CE?

Here’s the simple formula to convert from BP to BC/AD or BCE/CE:

BC, AD, BP, BCE, CE, KA, CAL, CIRCA: WHAT’S THE DIFFERENCE? A Good Library agoodlibrary.com agoodlibrary

Example 1:

Convert 4000 BP to BC/AD or BCE/CE system.

4000 – 1949 = 2051 BC

Example 2:

Convert 150 BP to BC/AD or BCE/CE system.

1950 – 150 = 1800 AD

The logic behind this formula: –

Example 1:

Convert 150 BP to BC/AD or BCE/CE system.

1950 – 150 = 1800

Since the result is positive, the result is –

150 BP = 1800 AD

This makes sense because the event happened in 1800 AD which happened 150 years before the present (1950)

Example 2:

Convert 4000 BP to BC/AD or BCE/CE system.

1950 – 4000 = -2050

Since the result is negative, we will subtract 1 from it. This is because there is no year 0. So, we have to count one year less as shown in Image 3.

So, our answer is 2051 BC.

4000 BP = 2051 BC.

Please note that this conversion is only valid for the years that happened on or before 1950 AD.

Why use BP and BC together?

When scientists use Carbon Dating to find out the date, the result is the age of the material as of today’s date. But, the date is not precise and needs further calibration. This date in BP is then converted to BC. So, it has become a common practice to mention both the carbon date and the calibrated date.

What is ka?

The acronym ‘ka’ is short for ‘kilo annum’ or ‘a thousand years’. ‘kyr’ also stands for ‘thousand years’ k- being the prefix denoting ‘Kilo’.

(Just how ‘Kilo’ refers to 1000 in other measurements.)

As per a Wikipedia entry, “ISO 80000-3 recommends usage of ka (for kilo annum), which avoids the implicit English bias of “year” by using a Latin root.”

This notation is generally used by people who have to deal with so old dates such as Geologists, Archeologists, Paleontologists, Anthropologists, etc.

For example, Late Stone Age is said to have occurred between 50 ka to 12 ka (50,000 and 12,000 years ago ~ BC 48000 to 1000 BC)

What is circa? (c. or ca.)

Circa is a Latin word that means ‘Around’ or ‘Approximately’. It is used to denote a date as a buffer. We know that the event happened around that date but are not sure exactly when.

Sometimes, you will see a date written as c. 300 B.C.E. That means the said event had happened approximately or around 300 years before the Common Era.

Here are some other Frequently Asked Questions about timelines:

Is it okay if we don’t use the notation?

It’s okay to drop the “AD” or “CE” when it’s not causing any confusion. But, it’s never okay to drop “BC” or “BCE”

  1. My friend Geeta was born in 1996.
  2. Julius Caesar was born in 100 BC.

How many BC years were there? What was the last BC year?

There are infinite numbers of BC years. Just like on the number line – the number before ‘0’ goes to negative infinity. So, what was the last BC year? Again, since the number is infinite, we cannot trace it back to the last BC year. It was perhaps when ‘time’ started – if there is any such thing. According to a study posted by NASA, “solar system settled into its current layout about 4.5 billion years ago”. So maybe we can take that as the last BC year.

What is the right word order & punctuation for the use of Calendar Notations?

AD Before the year AD 1525
BC After the year 5646 BC
CE After the year 2011 CE
BCE After the year 1134 BCE

In which timeline are we living – AD, BC, BCE, or CE?

According to the Gregorian Calendar that we are following here, we are living in 2021 CE (or, AD 2021). Unless the notations are changed in the future, we will continue to live in ‘CE’ or ‘AD’ till the end.

What is the point of C.E and B.C.E, since it still determines common eras by the birth of Christ?

Why Have Some People Adopted BCE/CE?

Why do we still have BC-AD despite having BCE-CE?

In the book ‘Pondering the Passion’, Cunningham and Starr (1998) mentioned that “B.C.E./C.E. …do not presuppose faith in Christ and hence are more appropriate for interfaith dialog than the conventional B.C./A.D.”

Basically, BCE-CE is a more secular and less-Christianity-oriented name of BC-AD. The traditional BC-AD system makes the birth of Jesus Christ and thus, the Christian religion the center point of the history of mankind. Every event is marked with the reference to Christ’s birth.

It was later found that Jesus Christ was born in or before 4 BC. Therefore, the calculations of AD-BC are not really based on his correct birth period. So, even though the current calculating system of BC-AD remains constant, calling it ‘the common era’ instead of ‘birth of Jesus’ is accepted by many.

The political battle “AD-BC v/s BCE-CE” has been there ever since the new system began. While supporters say that “BCE-CE” is more inclusive and secular, opponents believe that it is offensive to Christians. The opponents also claim that it makes no difference since the reference point remains the same.

In the BC-AD system, BC stands for English words “Before Christ” while AD stands for Latin words “Anno Domini.” CE-BCE doesn’t constrain itself to one particular religion. Therefore, experts believe that the acceptance should be global.


So, we are all living in AD 2021 which means 2021 years after the said birth of Jesus later to be named the Common Era. If there is any doubt, please contact us through the contact page or mail us at hello@agoodlibrary.com.

Also, as promised, the YouTube video with an even better explanation will be published tomorrow on our channel. Please refer to the schedule given in the sidebar (for desktop users, or below the article for mobile users) for the upcoming content on this topic.

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