Why December 25th?

Was that the ACTUAL birth date of Jesus?

In short, the answer is... probably not. There is a slim change that Jesus was born in late December due to the cold Winter weather. It is more likely that Jesus was born in the northern hemisphere Spring-Autumn (since the shepherds were in the fields and in Winter this would be improbable). Furthermore, the census would have been called during these warmer months due to the travel required.

The precise date of Jesus' birth is lost to history.

So... Why do we celebrate on December 25?

Simply, early Christians wanted a consistent date to remember the birth of Christ. Why not December 25?

There was significance in the date selected (I'll post why this is the case tomorrow).

In fact, depending which calendar you acknowledge (the Julian or the Gregorian) and what tradition you are attached to, Christmas is celebrated on alternate dates (such as January 7 in many Orthodox and Coptic Churches and January 10 in the Armenian Church).

Whilst we are in the realm of dates, Jesus wasn't born in 1AD.

The bloke who devised the modern division of BC/AD, a monk by then name of Dionysius Exiguus, miscalculated by a few years.

First, Herod the Great died in 4BC, and he is mentioned in the birth narratives.

Second, due to the multiple positions that Quiuinius held and the amount of time that a census took to span the Roman empire, we are fairly confident that Jesus was born somewhere around 7-4"BC." We know this due to the information we are given at the start of Luke 2 where we are told about Quirinius, who was the Roman governor of Syria, and the census that required Joseph and Mary to go to Bethlehem.