Calendars and time
Julian Calendar
Direct answer
Julian Calendar: The Julian Calendar is the solar calendar introduced under Julius Caesar with a leap day every fourth year.
The Julian Calendar uses a regular four-year leap cycle and preceded the Gregorian reform.
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At a glance
- Found in
- Calendars & Timekeeping
- Related
- Calendar, Solar Calendar, Lunar Calendar, Lunisolar Calendar
The Julian Calendar uses a regular four-year leap cycle and preceded the Gregorian reform.
A cycle or timeline schematic for comparing the named timekeeping concept.
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The story behind Julian Calendar
The calendar took effect in the Roman world in 45 BCE and was later replaced for civil use at different times in different places.
Why Julian Calendar matters
Julian Calendar’s average year is slightly longer than the seasonal year, causing calendar dates to drift gradually relative to the equinoxes.
How to read Julian Calendar
Julian Calendar speaks to historical records and communities that retain it for liturgical dates, and state conversions clearly.
Julian Calendar in practice: an example
A historical source dated in the Julian calendar can differ by several civil days from its Gregorian equivalent.
Where readings of Julian Calendar go wrong
The usual misreading is to confuse the Julian Calendar with Julian Date, which is a continuous astronomical day count.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Introduction to Calendars - Calendar definitions and the astronomical basis of solar, lunar, lunisolar, Julian, and Gregorian systems.
- U.S. Naval Observatory: Julian Date Converter - Official explanation and conversion service for Julian dates and civil calendars.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Convert historical calendar dates
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More in Calendars & Timekeeping
- Proleptic Julian Calendar
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Common questions
What is the Julian Calendar?
The Julian Calendar is the solar calendar introduced under Julius Caesar with a leap day every fourth year.
What do people get wrong about the Julian Calendar?
The usual misreading is to confuse the Julian Calendar with Julian Date, which is a continuous astronomical day count.
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