Across everyday life, scholarship and science, people rely on a handful of era labels to describe years. Some are closely linked to the Gregorian and Julian tradition, while others remain widely used for religious or civil purposes in different regions.
1) International-style era labels (Gregorian/Julian tradition)
BC and AD
These are long-established year markers meaning “Before Christ” and “Anno Domini” (literally, “in the year of the Lord”). The AD numbering system is commonly associated with Dionysius Exiguus in the 6th century, and it later became better known in European chronology through writers such as Bede.
BCE and CE
These stand for “Before Common Era” and “Common Era”. They do not change the maths of dating: the numbering matches BC/AD exactly. In other words, 2025 CE is the same year as AD 2025—only the label differs. The main reason they are used is to keep the familiar international numbering while adopting wording that is more religiously neutral.
BP (Before Present)
BP is chiefly used in scientific contexts, especially archaeology, geology and radiocarbon dating. Here, “present” is not today; it is fixed at 1950. So, 1000 BP corresponds to 950 CE.
2) Religious and civil eras still widely used
AH (Anno Hegirae / Hijri)
A lunar Islamic year count that begins from the Prophet Muhammad’s Hijra (migration), dated to 622 CE.
AM (Anno Mundi)
“Year of the world” dating systems found in some Jewish and Christian chronologies.
SE / Śaka Era (often called Saka Samvat)
A historic Indian era that also provides the year numbering used in India’s national calendar (the Indian national calendar / Saka calendar). In this system, Śaka year 0 aligns with 78 CE.
VS (Vikram Samvat)
A traditional Indian era used broadly, particularly in the north and west. It is typically counted from around 57 BCE, meaning the Vikram Samvat year is roughly 56/57 years ahead of the Gregorian year, depending on the month and the New Year convention being followed.
Why the Term “Common Era” Exists
The phrase “Common Era” is described as “common” because it keeps the most widely shared international year numbering—the same sequence used with AD—without naming Christ in the label. In practical use, CE/BCE helps the same dating system work smoothly in multi-faith and multi-national environments, including academia, diplomacy, science, global media and international organisations, while leaving the underlying calendar calculations unchanged.