Calculating Christ's Birth: Biblical Evidence for December 25

I asked a simple question many of us have heard all our lives: can we know when Jesus was born? I’ve often heard, “We can’t; we just picked a day.” That always bothered me, because Scripture says Jesus came in the “fullness of time.” So I went back to the text, leaned on help I received from my friend, a former Jewish rabbi, and traced both history and Scripture to see what they might say. Early Christian writers like Justin Martyr and Tertullian pointed to Roman census records as witnesses to the timing of Jesus’ birth. Later, Julius in Rome assigned December 25 from those records. Much was lost when Rome was sacked, but those early references remain.

Then we followed the Bible’s details. Luke 1 tells us Zechariah served in the temple during the “course of Abijah.” First Chronicles lists that course, and Exodus tells us the Jewish year begins with Nisan (mid-March). Counting forward places Zechariah finishing his course around mid-July. Luke says Elizabeth conceived “after those days.” Six months later Gabriel comes to Mary; that puts Jesus’ conception around mid-January. Nine months lands you mid-October—unless you account for something many miss: after the exile, the priestly courses were reorganized (Nehemiah 12). Abijah’s course moved from eighth to twelfth. Add those four courses, and you shift forward to mid-December. Human gestation averages 280 days—nine months plus ten days—bringing you to December 25. Luke quietly nods to this when he writes, “the days were accomplished that she should be delivered.”

Could I be off by a day or two? Sure. Just ask my wife. But when Scripture’s details, history’s witnesses, and simple biology line up, December 25 is not only plausible; it’s beautiful. And yet the point is not to win a date debate. Galatians 4 says the Father sent His Son “in the fullness of time… to redeem” and to give us adoption. That’s the aim. I’m glad we pick a day and celebrate. More than a date on a calendar, it is the day heaven joined earth so that slaves could become sons and daughters.

Key Takeaways

• 1. God moves in the fullness of time. God is not hurried and not late. He weaves timing through empires, censuses, and temple schedules to carry out His purposes. The quiet precision of His providence invites trust when our clocks feel broken. Waiting is not wasted; it is how He readies us for the moment He has prepared.
• 2. Scripture’s small details carry big weight. A phrase like “course of Abijah” looks minor until you follow it. God hides wisdom in the margins, training us to read slowly and listen well. Careful attention turns information into amazement and worship. Let the text shape your patience as much as your conclusions.
• 3. Faith welcomes history, calendars, biology. Truth does not fear scrutiny; it welcomes it. When Scripture and creation sing the same tune, confidence deepens, not shrinks. Bringing disciplines together can steady the heart in a skeptical age. Hold conclusions humbly, but don’t be afraid to think hard.
• 4. Advent aims at adoption and redemption. The calendar question matters less than the relational result. The Son came so slaves could become sons and daughters with a new name and a new home. Live like the adopted: free to draw near, free to obey, free to rejoice. Celebrate the date by embodying the gift.
• 5. Honor the hidden months of waiting. Elizabeth and Mary carried promises long before they were visible. Much of God’s work grows in secret places and silent stretches. Trust that unseen grace is still real grace. Keep walking, praying, and preparing while God forms what you cannot yet hold.

1. What specific facts about Zechariah’s service does Luke give (his family line, his “course,” and what he was assigned to do)? How does Luke link those facts to Elizabeth’s conception?
2. How does Luke describe the timing between Elizabeth’s pregnancy and Mary’s encounter with Gabriel? Which phrase tells us that timing?
3. Which small details in these verses stand out as unusually specific (names, numbers, phrases like “after those days,” “in the sixth month”)? Why might Luke include them?
4. How does Luke show Elizabeth’s and Mary’s physical and emotional responses to these events (e.g., hiding, haste, the baby leaping)?

1. What might Luke intend the reader to understand by naming Zechariah’s “course of Abijah”? How does that detail function in Luke’s larger narrative about Jesus’s origins?
2. How should the phrase “after those days” be read in context — as immediate, approximate, or theologically significant timing? What difference does that reading make for the sermon’s chronology?
3. The preacher connected timing in Luke with historical calendars and biology. What are the strengths and limits of using these kinds of external details (history, calendar systems, human gestation) to interpret Luke’s account?
4. Luke emphasizes concrete, ordinary things (a priest’s schedule, a woman’s pregnancy). What theological point might Luke be making by giving the nativity such everyday details?

1. When has God’s timing felt “late” to you? Describe a recent season when you were tempted to rush or to doubt. What one small practice (a prayer, a Bible passage to re-read, a person to speak with) could you try this week to cultivate trust that God works in the “fullness of time”?
2. The sermon urged reading “slowly” and noticing small details. Pick one short passage (maybe Luke 1 again). What is one tiny detail you usually skip over? What will you do this week to pay attention to it (read aloud, look up background, journal a reflection)?
3. The preacher used history and biology to strengthen confidence in the gospel. When someone in your life is skeptical, what is one way you could gently bring together Scripture, reason, and observable reality to discuss faith without being defensive?
4. The heart of Advent, the sermon said, is adoption and redemption. Name one concrete way you can act like an adopted child of God this week (a specific prayer habit, an act of obedience, a courageous step toward someone you’ve avoided). When will you do it?
5. Elizabeth and Mary carried hidden promises before anything was visible. What is one “hidden” promise, call, or waiting-season in your life right now? What are three small, practical steps you can take to keep preparing while you wait (people to ask for prayer, a habit to form, a practical task to accomplish)?
6. We celebrate a date to remember a deeper reality. This Advent season, choose one day to celebrate with gospel intentionality. What will you do on that day that is different from your normal routine (who will you invite, what will you give away, what will you fast from, what will you commemorate in family or personal worship)?
7. The sermon balanced humility about exact dates with boldness to think and examine evidence. In your faith conversations, where do you need to be more humble about what you don’t know, and where do you need to be more willing to think carefully and offer reasons for your hope? Identify one relationship where you can practice both this week.