DECEMBER 25 CALCULATION HYPOTHESIS

PART OF SERIES, "PASKO 2025: DISCOVER THE CHRISTMAS"

Author: Ken Klark L. Flores

Photo: Soraya / Pinterest

Introduction

There are many people are questioned, "What's the basis of December 25 as Christmas Day?" and "Why December?"

Calculation Hypothesis

The "calculation hypothesis" is a prominent scholarly theory used to explain why December 25 was chosen as the date for Jesus' birth. This argues the date was derived through independent theological and symbolic arithmetic by early Christians. 

The hypothesis, first substantially proposed by Louis Duchesne in 1889, suggests that early Christians determined Jesus’ birth date by working forward from the date they believed he was conceived (Caro et al., 2022). Some scholars and early traditions identify this temple service with Yom Kippur (the Day of Atonement), which occurs on Tishrei 10 (typically late September). Zechariah was serving in the "Holy of Holies" (or offering incense nearby), which occurred during this high holy month. 

Date and Text

The biblical text states that Mary conceived Jesus (the Annunciation) in the sixth month of Elizabeth's pregnancy with John. Early Christians also believed March 25 was the date of the Crucifixion, adhering to an ancient Jewish belief that prophets died on the same day they were conceived (living an "integer number of years") (Was Jesus Really Born Dec. 25? - Arlington Catholic Herald, 2022).

St. Hippolytus of Rome, writing around 235 CE, calculated Jesus' birth on December 25th by linking it to the creation of the world and Christ's conception/death. He connected the birth to the creation date (March 25th) in his Chronicon, marking Jesus' conception on Passover and birth 9 months later in his Canon, establishing the December 25th date long before it became widely adopted (fairfieldthinkspace, 2023; Stephens, 2022).

Some attempt to determine the date by tracing the service of the priestly course of Abijah (Zechariah's division), which could potentially place the birth in late December or January, though these calculations are often considered speculative.

The 25th of Pachon (or Paoni) was an ancient Egyptian date, roughly May 20th in our calendar, noted by early Christians like Clement of Alexandria (c. 200 AD) as the supposed day of Jesus's birth, long before December 25th became the universal date for Christmas, which was later linked to the Roman winter solstice and the dies Natalis Solis Invicti (Birthday of the Unconquered Sun) (Mcgowan, 2019).

In the calendar used by the compilers of the Apostolic Constitutions (likely a Syro-Macedonian calendar that started the year around the autumnal equinox, which aligned with the Roman October), the "ninth month" would correspond to the Roman month of December. Therefore, the date specified is December 25th, which aligns with the traditional date of Christmas in Western Christianity. The passage in the Apostolic Constitutions (Book V, Section 3, Chapter 13) states: "Brethren, observe the festival days; and first of all the birthday which you are to celebrate on the twenty-fifth of the ninth month" (Philip Schaff: ANF07. Fathers of the Third and Fourth Centuries: Lactantius, Venantius, Asterius, Victorinus, Dionysius, Apostolic Teaching and Constitutions, Homily, and Liturgies - Christian Classics Ethereal Library, 2025).

Criticism

Critics frequently point to the Gospel of Luke to argue that a winter birth is improbable. Luke 2:8 describes shepherds "living out in the fields, keeping watch over their flock by night". Critics argue that December in Judea is too cold and rainy for this; sheep were typically brought into shelters from November until March. Luke 2:1–4 records Mary and Joseph traveling to Bethlehem for a census. 

Critics contend that Roman authorities would not have ordered a census in winter, when travel conditions were poor and temperatures could drop below freezing (Biblical Evidence Shows Jesus Christ Wasn’t Born on Dec. 25, 2004). Defenders note that the Judean climate is Mediterranean; while rainy, it is not consistently freezing, and certain types of sheep (specifically those for temple sacrifice) might have been kept outdoors year-round.

Reference

Caro, L. D., Greca, F. L., & Matricciani, E. (2022). Dating the Birth of Jesus Christ on Hanukkah. Open Journal of Social Sciences, 10(10), 304–317. https://doi.org/10.4236/jss.2022.1010020

Was Jesus really born Dec. 25? - Arlington Catholic Herald. (2022, February 3). Arlington Catholic Herald. https://www.catholicherald.com/article/columns/was-jesus-really-born-dec-25/

‌fairfieldthinkspace. (2023, December 21). Calculating Christmas: Hippolytus and December 25th. Tumblr. https://thinkspace.fairfield.edu/post/737347927637377024/calculating-christmas-hippolytus-and-december

Biblical Evidence Shows Jesus Christ Wasn’t Born on Dec. 25. (2004, December 3). United Church of God. https://www.ucg.org/good-news/good-news-magazine-november-december-2004/biblical-evidence-shows-jesus-christ-wasnt-born-dec-25

Stephens, R. A. (2022, December 21). Why December 25? – The Lutheran Witness. The Lutheran Witness. https://witness.lcms.org/2022/why-december-25/

‌Was Jesus Born December 25th? (n.d.). Catholic Answers. https://www.catholic.com/magazine/print-edition/was-jesus-born-december-25th

‌Mcgowan, A. (2019, December 10). How December 25 Became Christmas. Biblical Archaeology Society. https://www.biblicalarchaeology.org/daily/people-cultures-in-the-bible/jesus-historical-jesus/how-december-25-became-christmas/

‌Philip Schaff: ANF07. Fathers of the Third and Fourth Centuries: Lactantius, Venantius, Asterius, Victorinus, Dionysius, Apostolic Teaching and Constitutions, Homily, and Liturgies - Christian Classics Ethereal Library. (2025). Ccel.org. https://www.ccel.org/ccel/schaff/anf07.ix.vi.iii.html