What are the ages of BC and AD?

AD is often represented by A.D. (Latin abbreviation of Anno Domini, meaning "the year of the Lord's birth"), while BC is represented by B.C. (abbreviation before Christ, meaning "before Christ"), which is usually written before AD.

"A.D." came into being in the 6th century when Christianity was prevalent. At that time, monks attached everything to Christianity in order to expand the ruling power of the church. In 525 AD, a monk named Dionysius proposed that Jesus was born in 284 years under the rule of Diocletian, the king of ancient Rome, in order to predict the date of Easter seven years later (that is, in 532 AD), and advocated taking the year of Jesus' birth as the starting point, which was strongly supported by the church. In 532 AD, the church took 284 BC as the first year of AD and used this chronology in the church. By 1582, the Pope had formulated the Gregorian calendar and continued to adopt this chronology. The Gregorian calendar is a pure solar calendar, originally used to calculate "Easter". The Gregorian calendar is called the Gregorian calendar because of its high accuracy and international use. The so-called "AD" refers to the Gregorian calendar era or the first year of AD.

In modern times, due to the universality and standardization of calendar years, in order to avoid non-Christians' resentment and cultural and ideological disputes, "B.C.E" and "C.E." are more and more commonly used in English to mean "BC" and "AD" respectively. "C.E." is the abbreviation of "Common Era", which means "A.D.", while "B.C.E" is the abbreviation of "Before Common Era", which means "BC".