Despite our modern calendar having dates specified by AD (in the year of our Lord) and BC (before Christ), Jesus was not born in the year 0. In fact, there was no year zero.
According to our calendar, the year 1 BC was followed by the year AD 1. Apparently a Scythian monk, Dionysius Exiguus, forgot to include the year 0 between 1 BC and AD 1, when he was instructed to develop a new calendar in the 6th century AD. This anomaly must be accounted for when calculating time periods that begin BC and finish AD.
This hapless monk also overlooked some years of the Roman emperor, Augustus. Thus, the birth of Jesus is actually dated BC! The most likely date is around 5 or 6 BC. Despite the celebration of Christmas, we don’t actually know what time of year he was born.
For more detail on biblical chronology, see The Times.