What does the Bible say about when Jesus was born? It’s all in Luke’s Gospel. And it starts with John the Baptist.
The angel announces John’s conception on the day his father (one of the Temple priests) enters the Holy of Holies. That’s a once a year thing, on Yom Kippur (the Day of Atonement). Following the Hebrew lunar calendar, that happens in late September/early October.
When Mary says yes to God, the angel says “BTW, John’s mother is 6 months pregnant.” That puts the conception of Jesus in late March/early April (tradition says March 25).
Add 9 months and Jesus is born in late December/early January.
Which means that December 25 is definitely in the ballpark.
A lot of websites talk about the Emperor and/or the Pope picking December 25 when Christianity was legalized by the Roman Empire in the mid-300’s. With the idea being that December 25 was chosen to compete with pagan religions.
Actually, they were just recognizing a tradition that people were writing about in the early 200’s.
And those writers? They were writing about a tradition that dates from the generation of Christians after the Apostles. The same generation that Luke was part of (who wrote his Gospel sometime between 80-100).