From:
https://onepeterfive.com/dates-years-birth-death-christ/
"First Point: John the Baptist was conceived around late September of 3 B.C. near the Day of Atonement.
A
Hebrew calendar shows that the Day of Atonement (also called Yom Kippur) was on Sep. 19, 3 B.C. It is the contention of this article that the Baptist was conceived around this time, when St. Zachary was ministering in the Temple. In other words, the story of our salvation began on the ancient Day of Atonement commanded by God, which is fitting. It is here that the Gospel events recorded by St. Luke in chapter 1 really begin to take off.
Luk 1:5 “There was in the days of Herod, the king of Judea, a certain priest named Zachary, of the course of Abia; and his wife was of the daughters of Aaron, and her name Elizabeth.”
As Dr. Marshall
explains, a course of Abia occurs in September, and there is evidence in this passage to suggest that the time is around the Day of Atonement, when the high priest goes into the holy place, as we read in Ex. 30:10, Lev. 16:3, Heb. 9:7, etc.
Second Point: Jesus Christ Our Lord was conceived around six months after St. John the Baptist.
Moreover, we know from the same chapter that Our Lady conceived Christ about six months after St. Elizabeth conceived the Baptist. For the Angel says
(36), “And behold thy cousin Elizabeth, she also hath conceived a son in her old age; and this is the sixth month with her that is called barren: [37] Because no word shall be impossible with God.”
Now, if the Baptist was conceived in late September, Christ the Lord would have been conceived in late March. Similarly, we can reasonably deduce that the Baptist would be born around late June, nine months after conception.
Third Point: Therefore, Christ Our Lord was conceived on March 25, 2 B.C. and born Dec. 25, 2 B.C.
It is an interesting point that
“the twenty-fifth day of the ninth month, that is, the month of Kislev” (1 Mac. 4:22) was already held in honor as a Festival of Light. It is the Feast of Dedication in winter mentioned by St. John (10:22). The Hebrew calendar begins in March-April in Nisan, so its ninth month roughly comes to our twelfth month, December, in most years. It is highly fitting that the 25th day of the 12th month on the Christian calendar should have been set apart for Christ, “The Light of the World” (Jn. 8:12), to make His entrance into the world.
The Baptist being born in late June, as shown in the Second Point, Christ Our Lord certainly would have been born around late December. The witness of Tradition, of very early historical Tradition, is clear on this point.
Bp. Theophilus (115–181 A.D.) stated: “We ought to celebrate the birthday of Our Lord on what day soever the 25th of December shall happen.”
Saint Hippolytus (170–240 A.D.) wrote: “The First Advent of our Lord in the flesh occurred when He was born in Bethlehem, was December 25th, a Wednesday, while Augustus was in his forty-second year, which is five thousand and five hundred years from Adam.”
St. Augustine finally confirms: “But he was born, according to Tradition, upon December the 25th.”
In sum, Our Lord’s date of birth:
Dec. 25, 2 B.C. Our Lord’s date of crucifixion:
April 3, 33 A.D.
Therefore, the first Easter:
April 5, 33 A.D. The 50th day, the first Pentecost:
May 24, 33 A.D."
