Most theologians and religious historians believe that Yeshua of Nazareth (Jesus) was born during a Fall -- or less likely during a Spring, sometime between 7 and 4 BCE.However, we have seen estimates as as early as the second century BCE and as late as 4 CE.
CE and BCE are notations that are not based on religion or myth. The AD/BC notation was first proposed by the monk Dionysius Exiguus (Dennis the Little) in the year 525 CE.
In 1422 [CE], Portugal became the last country of western Europe to adopt the Anno Domini..." notation.
Until the eighteenth century CE, the term Anno Salutis ("in the year of salvation") or Anno Nostrae Salutis ("in the year of our salvation"), Anno Salutis Humanae ("in the year of the salvation of men"), and Anno Reparatae Salutis ("in the year of accomplished salvation") were sometimes used in place of AD. "Only Rosten's Joys of Yiddish comments on these abbreviations that they have long been popular with Jewish scholars who were uncomfortable with a christological dating system. Unfortunately I can find no information to hand on just how long this has been a common practice, or if it indeed originated with Jewish scholars.
There are many religious calendars in existence, but each is normally in use in one region of the world -- typically by followers of a single religion.
Almost all of the world's religious calendars are based on religion, astrology, or myth: The division between BC/BCE and AD/CE is not based on religious considerations.