Calendar era

period of time elapsed since one epoch of a calendar and, if it exists, before the next one

A calendar era is the year numbering system used by a calendar. The Gregorian calendar for example numbers its years in the Western Anno Domini system (the Coptic Orthodox and Ethiopian Orthodox churches have their own Christian eras). The instant, date, or year from which time is marked is called the epoch of the era. There are many different calendar eras such as Saka Era.

2021 in various calendars
Gregorian calendar2021
Ab urbe condita2774
Armenian calendar1470
Assyrian calendar6771
Bahá'í calendar177–178
Balinese saka calendar1942–1943
Bengali calendar1428
Berber calendar2971
British Regnal year69 Eliz. 2 – 70 Eliz. 2
Buddhist calendar2565
Burmese calendar1383
Byzantine calendar7529–7530
Chinese calendar庚子(Metal Rat)
4717 or 4657
    — to —
辛丑年 (Metal Ox)
4718 or 4658
Coptic calendar1737–1738
Discordian calendar3187
Ethiopian calendar2013–2014
Hebrew calendar5781–5782
Hindu calendars
 - Vikram Samvat2077–2078
 - Shaka Samvat1942–1943
 - Kali Yuga5121–5122
Holocene calendar12021
Igbo calendar1021–1022
Iranian calendar1399–1400
Islamic calendar1442–1443
Japanese calendarReiwa 3
Javanese calendar1954–1955
Juche calendar110
Julian calendarGregorian minus 13 days
Korean calendar4354
Minguo calendarROC 110
Nanakshahi calendar553
Thai solar calendar2564
Tibetan calendar阳金鼠年
(male Iron-Rat)
2147 or 1766 or 994
    — to —
(female Iron-Ox)
2148 or 1767 or 995
Unix time1609459200 – 1640995199

In ancient times, regnal years were counted from the year a new monarch took the throne. This makes ancient timelines very difficult to reconstruct, because they are based on separate and scattered king lists, such as the Sumerian King List and the Babylonian Canon of Kings. In East Asia, having era names based on ruling monarchs ended in the 20th century except for Japan, where they are still used.