You’ll often hear people say that Jesus was not born on December 25. Some say he was likely born in the Spring and that Christmas is just a Christianized pagan holiday.
Here’s the truth: the early Church celebrated Christmas on December 25 because that’s the day many thought Jesus was born.
They had two arguments for this date.
First, they believed that Jesus was crucified on March 25 (given when Passover normally falls), and there was a tradition that Jesus died the same day he first entered the world (his conception). Nine months later after March 25 is December 25.
Second, and most importantly, Scripture provides strong evidence that December 25, or a date near that, is the date Jesus was born.
The Gospel of Luke tells us the angel Gabriel revealed to Zechariah that his wife Elizabeth would conceive John the Baptist while Zechariah was performing his priestly duties on the Day of Atonement, also known as Yom Kippur. That Jewish holy day always falls in late September or early October.
Luke also tells us that, after Gabriel announced to Mary that she would conceive Jesus, she went in haste to visit Elizabeth, and that Elizabeth was in the sixth month of her pregnancy.
Now do the math: If Elizabeth conceived in late September, and Mary visited her in her sixth month, this means Mary conceived Jesus and visited Elizabeth in late March. And if Mary conceived Jesus in late March, that places his birth in late December.
So it’s very possible the Early Church got it right, and December 25 really is Jesus’ birthday!
For an in-depth analysis of Christ's birth, learn more on Catholic Answers.