Have you ever noticed that the months in the Bible don’t match the calendar on your wall? Or wondered how our modern calendar even came to be?
Let’s take a quick walk through history to see how time was measured in the Bible, how it changed over the centuries, and why it still matters today.
How Did Ancient Calendars Measure Time?
Ancient cultures didn’t all track time the same way. Most calendars followed one of three systems:
Solar Calendars
Solar calendars follow the sun and are based on the earth’s rotation around it.
The ancient Egyptians used a solar calendar with 365 days in a year.
Lunar Calendars
Lunar calendars follow the phases of the moon.
The Sumerians used a lunar calendar with 12 months, each lasting 29–30 days.
Lunisolar Calendars
Lunisolar calendars combine both systems.
The biblical (Hebrew) calendar is lunisolar—months follow the moon, while years stay aligned with the sun.
How Did We Get Our Modern Calendar?
Our modern calendar traces back to the Roman Empire.
The Julian Calendar
Introduced in 46 BC by Julius Caesar, the Julian calendar standardized time across the empire and followed the solar year. Some Eastern Orthodox churches still use it to determine holidays today.
The Gregorian Calendar
In 1582, Pope Gregory XIII introduced the Gregorian calendar to correct small timing errors. This included refining leap years and adjusting how Easter is calculated.
Today, the Gregorian calendar is the most widely used calendar in the world.
How Are Days and Weeks Measured?
Different calendars even define days and weeks differently.
Gregorian Calendar
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Days: Midnight to midnight
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Weeks: Seven days, traditionally starting on Sunday
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Day names: Based on celestial bodies from ancient astronomy
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Sunday – Sun
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Monday – Moon
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Tuesday – Mars
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Wednesday – Mercury
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Thursday – Jupiter
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Friday – Venus
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Saturday – Saturn
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Hebrew Calendar
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Days: Sunset to sunset
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Weeks: Seven days, centered on the Sabbath
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Day names: Counted in relation to the Sabbath
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Sunday – First day
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Monday – Second day
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Tuesday – Third day
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Wednesday – Fourth day
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Thursday – Fifth day
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Friday – Sixth day
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Saturday – Sabbath
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Where Did the Month Names Come From?
Our modern calendar has 12 months, each lasting 28–31 days. Their names come from Roman gods, leaders, and Latin numbers:
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January – Janus
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February – Roman festival Februa
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March – Mars
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April – Aphrodite
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May – Maia
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June – Juno
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July – Julius Caesar
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August – Augustus Caesar
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September – Seventh month
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October – Eighth month
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November – Ninth month
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December – Tenth month
How Are Years Measured Today?
Years on the Gregorian calendar are measured from the birth of Jesus.
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BC / BCE: Before Christ / Before Common Era
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AD / CE: “In the year of our Lord” / Common Era
Each year begins on January 1 and ends on December 31.
Why This Matters for Bible Study
Understanding how calendars work helps the Bible make more sense—especially feast days, timelines, and historical events. Seeing Scripture in its original time framework adds depth and clarity to your study.
👉 Want to explore this further?
Take a look at our Biblical Events Calendar and see how biblical time connects to the calendar you use every day.
